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9 


GROWTH  IN  TREES  AND  MASSIVE  ORGANS 

OF  PLANTS 


DENDROGRAPHIC  MEASUREMENTS 

By  D.  T.  MacDougal 


THE  GROWTH  RECORD  IN  TREES 

By  Forrest  Shreye 


THE  lIRHftPT  nr  •<; 
SFP  8  1924 

UNIVERSITY  Of  ILLINOIS 


mtOTV  Of  IM-OKIi*  UWUfr 


Published  by  the  Carnegie  Institution  of  Washington 

Washington,  May,  1924 


CARNEGIE  INSTITUTION  OF  WASHINGTON 

Publication  No.  350 


Copies  of  this  book  I 
first  issued 
MAY  16  1924  ^ 


Judd  &  detw eiler,  inc. 

WASHINGTON,  D.  C. 


5 

N\  \  A  ^  K, 


DENDROGRAPHIC  MEASUREMENTS. 

BY 


D.  T.  MacDougal. 


CONTENTS. 


PAGE. 

Scope  and  purpose  of  the  investigations .  3 

Duration  and  limit  of  growing-season .  5 

Growth  of  roots .  9 

Thickness  of  woody  layers  and  length  of  growing  season  of  No.  1 .  9 

Seasonal  activity  and  wood-formation  in  several  Monterey  pines .  10 

Experimental  investigations .  13 

Effects  of  breaking  the  conducting  system  by  girdling .  13 

Reduction  of  total  capacity  of  green  leaves  by  topping .  21 

Effects  of  defoliation .  24 

Path  and  rate  of  movement  of  liquids  in  stems  of  Monterey  pine .  29 

Reversible  variations  in  volume  independent  of  growth .  35 

Standardization  of  dendrograph  for  measurement  of  daily  equalizing  variations. .  37 

Course  of  the  daily  equalizing  variation  in  trees .  39 

Daily  variations  in  volume  of  inner  woody  cylinder  of  a  Monterey  pine  tree .  41 

Growth  of  the  Arizona  pine .  42 

The  Mexican  white  pine .  43 

Relation  of  Arizona,  Mexican,  and  Chihuahua  Pines  to  seasonal  variations .  44 

The  yellow  pine .  46 

The  California  redwood .  47 

The  Arizona  walnut .  50 

Growth  of  nuts  of  Juglans  major .  52 

The  Arizona  ash .  53 

The  palo  verde . 55 

The  Bagote .  55 

The  sycamore .  56 

The  Carolina  poplar .  56 

MacDougal’s  poplar .  56 

The  Arroyo  willow .  58 

Measurements  of  yearly  increase  in  circumference  of  tree-trunks  by  means  of  the 

dendrometer .  58 

The  Sahuaro .  60 

Growth  of  Opuntia .  68 

Variations  in  leaves  of  M esembryanthemum .  74 

Growth  of  potato  tubers .  75 

Growth  of  the  squash .  78 

Summary .  81 


2 


^  S  £  4-  V,3  5  o  cL  1  v\  *5  ,  c.  ft  -WtT, 


DENDROGRAPHIC  MEASUREMENTS. 

SCOPE  AND  PURPOSE  OF  THE  INVESTIGATIONS. 

Various  features  of  growth  in  organs  of  widely  divergent  morphology 
have  been  discussed  by  the  senior  author  in  papers  published  since  1916. 
Additional  records  and  measurements  of  the  changes  in  volume  of  meso- 
phytic  leaves,  herbaceous  stems,  tree-trunks,  succulent  shoots  of  cacti,  suc¬ 
culent  leaves  of  Mesembryanthemum,  leguminous  pods,  large  berry-like 
fruits,  melons,  tubers,  and  nuts  are  presented  in  this  paper. 

These  studies  have  been  carried  on  concurrently  with  experimental  work 
on  the  water  relations  of  biocolloids,  of  interest  in  connection  with  the  con¬ 
stitution  of  the  plants,  and  some  attention  has  also  been  paid  to  the  influ¬ 
ence  of  ions  of  the  common  salts  on  the  permeability  and  growth  of  cells. 

Interpretation  of  changes  in  volume  due  to  growth  has  been  made  with 
reference  to  the  distinctly  two-phase  aspect  of  this  process  in  plants.  The 
cell  or  protoplast  of  the  plant  is  in  its  earliest  stage  a  continuous  or  solid 
mass  of  jelly-like  colloid.  Additions  to  its  mass  are  made  by  the  formation 
of  new  particles  of  the  materials  of  which  it  is  composed.  These  include 
proteins  or  albumins,  pentosans,  soaps,  and  fatty  substances.  Despite  the 
fact  that  the  presence  of  substances  of  all  of  these  groups  is  well  known  to 
all  experimental  workers,  yet  most  of  the  literature  dealing  with  the  consti¬ 
tution  of  protoplasm  treat  living  matter  as  if  it  were  chiefly  or  entirely 
albuminous. 

The  additions  to  the  mass  of  protoplasm  have  slight  effect  on  the  external 
measurements  of  a  plant.  The  chief  expansion  of  a  cell-mass  or  of  a  grow¬ 
ing  organ  is  due  to  the  distention  of  the  cells.  Clear  spaces  or  vacuoles  are 
formed  by  syneresis  in  the  mass  of  living  matter,  and  the  substances  dis¬ 
solved  in  the  water  which  fills  these  cavities  act  osmotically  in  pulling  in 
more  water,  with  a  resultant  expansion  to  a  volume  many  times  that  of 
the  embryonal  mass.  This  distention  is  not  accompanied  by  any  notable 
increase  in  the  amount  of  protoplasm;  the  distended  cell  may  have  actually 
less  than  the  original. 

The  rate  and  amount  of  the  distention  or  enlargement  is  determined  by 
the  osmotic  potential  of  the  substances  in  the  vacuoles.  Sugars,  amino 
acids,  etc.,  are  present,  and  some  salts.  Whether  the  salts  on  the  average 
furnish  much  of  the  osmotic  pressure  is  somewhat  doubtful.  The  larger 
part  is  probably  due  to  sugars  present.  The  rate  and  course  of  enlarge¬ 
ment  will,  however,  be  determined  largely  by  the  permeability  of  the  layers 
of  protoplasm,  and  the  wall  to  the  substances  in  the  vacuole.  The  per¬ 
meability  of  these  colloidal  layers  is  largely  determined  by  the  ions  of  the 
salts  in  the  medium  or  salt  solution,  and  the  implied  relation  is  one  of  the 
most  important  in  the  life  of  the  plant.  It  is  understood,  of  course,  that  it 
is  only  cells,  the  external  layers  and  walls  of  which  are  permeable  to  water, 
which  would  be  capable  of  changes  in  volume.  The  larger  particles  of  dis¬ 
solved  organic  substances,  such  as  sugars,  may  pass  through  them  slowly 
or  not  at  all,  while  the  smaller  and  more  swiftly  moving  ions  of  the  elec¬ 
trolytes  penetrate  at  various  rates. 

3 


555 


4 


DENDROGRAPHIC  MEASUREMENTS. 


It  has  been  found  that  the  electrolytes  cause  changes  in  the  colloidal 
layers  or  “membranes”  of  the  cell  which  alter  its  penetrability  by  other 
ions  or  substances,  including  those  to  which  are  due  osmosis,  turgidity,  and 
the  resultant  enlargement  of  the  cell.  The  material  which  may  thus  affect 
the  rate  and  course  of  growth  is  complex,  and  its  action  is  difficult  to 
arrange  under  any  simple  formula. 

A  large  share  of  the  work  described  in  the  present  paper  was  devoted  to 
growth  and  changes  in  volume  of  the  trunks  of  trees.  This  involved  not 
only  a  study  of  the  nature  of  growth  as  generally  characterized  above, 
but  also  made  necessary  a  consideration  of  the  mechanism  of  the  body 
of  a  tree.  The  embryonal  cell-masses  form  a  thin  sheet  on  the  outside 
of  the  woody  cylinder  and  run  into  the  growing  points  of  the  stem  and 
branches.  As  has  been  previously  pointed  out,  this  mass  of  growing  cells 
does  not  act  as  a  unit.  Cell-division  and  distention  of  cells  constituting 
growth  may  occur  in  some  but  not  in  all  of  the  points  with  embryonic 
cells,  and  the  sheet  of  cambium  encircling  the  trunk  may  likewise  show 
localized  activity. 

The  assembling  of  the  materials  necessary  for  the  organization  of  new 
protoplasm  and  the  development  of  new  cells  in  these  massive  bodies  neces¬ 
sitates  a  complicated  mechanism,  the  operation  of  some  parts  of  which  are 
but  dimly  comprehended.  The  electrolytes  enter  the  roots  in  an  amount 
and  at  a  rate  determined  chiefly  by  the  velocities  and  other  characters  of 
the  ions,  their  mutual  interferences,  and  their  effect  on  the  colloidal  lattice 
of  the  surfaces  of  the  root-hairs.  The  carbohydrates  are  formed  in  the 
leaves  in  connection  with  the  entrance  of  carbon  dioxide  from  the  air.  A 
movement  of  electrolytes  from  the  roots  to  the  leaves  may  be  accounted 
for,  but  at  the  present  time  the  passage  of  sugars  and  nitrogenous  material 
from  the  leaves  to  the  trunk  and  to  the  roots  offers  some  problems  in  the 
physics  of  diffusion  and  conduction  for  which  no  possible  or  plausible 
solutions  have  been  offered. 

Necessarily  much  attention  has  been  paid  to  the  influence  of  climatic 
features  upon  these  processes.  Some  attempt  has  been  made  to  correlate 
climatic  phases  with  the  amount  and  character  of  wood  formed  in  trunks, 
as  ordinarily  studied  in  cross-sections  as  “rings”  by  the  climatologist  inter¬ 
ested  in  climatic  fluctuations. 

Dendrographic  measurements  of  trees  were  begun  in  the  autumn  of  1918, 
and  have  been  so  extended  that  at  present  (close  of  the  season  of  1923) 
records  of  the  growth  of  trees  to  a  total  of  about  90  seasons,  representing 
21  species,  are  available,  in  addition  to  the  continuous  records  of  growth 
of  tubers,  fruits,  and  stems  of  other  plants  which  are  presented. 

The  dendrographic  measurements  made  during  the  first  three  years  of  the 
observations  were  of  a  wide  variety  of  species,  and  the  information  thus 
secured  forms  the  basis  of  a  possible  comprehension  of  the  behavior  of  tree- 
trunks  of  various  habits  and  morphological  types.  Later,  attention  was 
concentrated  on  the  conifers,  and  the  greater  number  of  in&truments  were 
used  on  the  Monterey  pine  ( Pinus  radiata ) ,  while  some  observations  on  the 
redwood  ( Sequoia  sempervirens )  begun  in  1921  were  continued  and  ex¬ 
tended  to  include  five  trees,  of  which  continuous  records  were  made  for 
periods  of  various  lengths  from  one  to  two  years. 


DURATION  AND  LIMIT  OF  GROWING-SEASON. 


5 


Analysis  of  growth  of  trees  in  different  habitat  complexes  uncovers  some 
correlations  between  daily  variations  and  growth  on  the  one  hand,  with 
stomatal  action  and  meteorological  phenomena  on  the  other.  Especial 
attention  has  been  given  to  the  direct  effect  of  rainfall  on  the  thickness  of 
the  layers  of  wood  formed,  which,  as  rings  seen  in  cross-sections  of  trunks, 
are  considered  as  records  of  climate  by  many  investigators.  That  the 
thickness  of  the  layers  is  not  always  primarily  determined  by  the  rainfall 
of  the  season  in  which  they  are  formed  might  be  expected.  Various  experi¬ 
mentally  induced  variations  in  the  water-supply  and  conductive  systems  of 
trees  have  been  made  for  the  purpose  of  determining  the  relative  and  direct 
effects  of  the  environic  components  and  of  the  mechanism  of  food-supply. 
Unseasonable  irrigation,  mechanical  girdling  of  trunks,  killing  of  a  basal 
section  of  trunks  without  removal  or  mechanical  damage  to  the  bark, 
decapitation,  defoliation  at  various  seasons,  the  injection  of  dyes,  and  other 
means  have  been  used,  with  results  as  described  on  the  following  pages. 

Measurements  of  the  variations  in  volume  of  other  organs,  such  as  the 
flat  joints  of  Opuntia,  which  display  a  behavior  much  like  the  trunks  of  the 
tree  cactus  ( Carnegiea ),  of  tubers  of  the  common  potato  during  their 
development,  of  the  nuts  of  Juglans,  coincidentally  with  observations  on  the 
trunks  of  the  trees,  and  of  the  fruit  of  the  squash  ( Cucurbita ) ,  have  been 
added  for  the  purpose  of  extending  the  study  of  the  variations  in  growing 
organs  caused  by  a  fluctuating  water-balance.  The  last-named  material 
also  illustrates  the  course  of  growth  in  a  structure  in  which  the  proportion 
of  water  to  the  dry  matter  rises  toward  maturity. 

DURATION  AND  LIMIT  OF  GROWING-SEASON. 

The  region  of  the  Coastal  Laboratory  is  at  the  upper  margin  of  the  frost 
belt,  freezing  temperatures  occurring  for  only  a  few  hours  annually,  and 
with  some  exceptions  in  which  the  thermometer  does  not  fall  so  low.  The 
principal  part  of  the  rainfall  comes  in  the  winter,  or  cooler  season,  so  that 
growth  begins  with  a  rising  temperature  accompanied  by  a  progressive 
decrease  of  soil  moisture.  The  summer  months,  in  which  the  soil  moisture 
is  at  a  minimum,  is  characterized  by  much  fogginess,  one  period  of  18  days 
without  direct  sunlight  being  recorded  at  the  Coastal  Laboratory. 

A  tree  does  not  react  as  a  simple,  unified  mass  of  living  matter,  as  some 
organs  may  awake  and  show  growth  with  the  remainder  of  the  body  in  a 
dormant  condition.  It  is  to  be  seen  that  in  an  equable  climate,  as  that  of 
Carmel,  the  opening  and  close  of  the  growing-season  may  be  very  indefinite. 

Thus,  in  the  winter  season  of  1922  and  1923  the  tips  of  roots  of  the 
Monterey  pine  lying  within  10  cm.  of  the  surface  showed  elongation  late 
in  November,  and  also  in  December,  and  apparently  were  active  through¬ 
out  the  rainy  season;  and  shoots  of  young  pines  also  showed  elongation 
throughout  the  winter  season,  so  that  the  total  amounted  to  as  much  as 
42  mm.  in  some  cases  by  January  8,  according  to  notes  furnished  by  Dr. 
W.  A.  Cannon.  Enlargement  of  the  stems  of  any  of  these  trees,  some  of 
which  were  but  10  cm.  in  diameter,  occurred  in  November  and  December 
1922,  and  growth  for  the  season  began  January  3.  The  larger  trees  remained 
inactive  in  this  member  until  much  later,  as  may  be  seen  in  Table  2. 


6 


DENDROGRAPHIC  MEASUREMENTS. 


Naturally,  the  close  of  the  season  is  marked  by  similar  irregularities,  the 
different  parts  becoming  inactive  at  different  times,  and  this  applies  also 
to  the  upper  and  lower  parts  of  the  trunk.  The  sheet  of  cambium  of  the 
trunk  apparently  awakens  at  once  so  far  as  the  observations  bear  on  this 
point,  but  growth  may  cease  in  one  part  while  it  is  still  in  progress  in 
another  place.  These  features  are  illustrated  by  the  dates  given  in  Table  1, 
in  which  the  seasons  of  activity  of  Monterey  pine  No.  1  are  given  from 
1919  to  1923,  inclusive. 

The  time  at  which  the  activity  of  the  cambium  resulted  in  enlargement 
of  the  trunk,  and  the  time  at  which  such  accretion  ceased  in  a  diameter  over 
a  meter  from  the  base  of  the  tree,  are  given  after  A,  and  the  same  dates  are 
given  after  B  for  a  diameter  8  meters  higher  on  the  trunk. 

A  dendrograph  of  the  initial  design  was  attached  to  the  trunk  at  A  in 
September  1918,  and  superseded  by  improved  patterns  in  such  manner  that 
a  continuous  record  could  be  maintained.  A  tracing  for  five  complete  years 
is  now  available  (September  1923).  The  instrument  was  attached  to  the 
trunk  at  B  in  January  1920,  and  the  record  for  four  growing-seasons  are 
available.  The  arrangement  of  the  instruments  was  figured  in  Publication 
307  (1921). 


Table  1. — Seasonal  activity  of  Monterey  pine  No.  1. 


Year. 

Beginning. 

Ending. 

Duration 
in  days. 

A 

1919 

Mar.  30 

Aug.  31 

153 

A 

1920 

Apr.  9 

Oct.  10 

184 

B 

1920 

Do. 

Oct.  1 

175 

A 

1921 

Jan.  25 

Oct.  16 

264 

B 

1921 

Jan.  26 

Oct.  10 

257 

A 

1922 

Feb.  7 

Sept.  16 

221 

B 

1922 

Do. 

Aug.  9 

182 

A 

1923 

Jan.  10 

Sept.  3 

236 

B 

1923 

Do. 

Do. 

236 

The  generalization  that  growth  is  initiated  on  the  upper  part  of  the 
trunk,  and  gradually  extends  downward,  finds  no  support  from  the  records 
given  above.  Enlargement  of  the  trunk  was  seen  to  begin  coincidentally 
near  the  base  of  the  trunk  and  at  a  place  8  meters  above  it.  On  the  other 
hand,  cessation  of  growth  might  occur  on  widely  separated  dates  in  the 
two  places. 

Thus,  in  1920  the  cambium  at  the  uppermost  location  in  No.  1  ceased  to 
enlarge  10  days  earlier  than  that  on  the  basal  part  of  the  trunk,  while  in 
1921  this  difference  was  but  6  days.  The  basal  part  of  the  tree  had  a 
growing-period  39  days  longer  than  that  of  the  upper  location  in  1922. 
About  5  weeks  later  some  activity  was  shown  in  both  places,  which  con¬ 
tinued  intermittently  throughout  the  winter.  The  beginning  and  end  of 
growth  was  simultaneous  above  and  below  in  1923. 

The  beginning  date  of  growth  was  seen  to  vary  through  73  days  of  the 
calendar  at  the  base  and  72  days  at  the  upper  location;  the  closing  date 
46  days  at  the  base  and  54  days  at  the  upper  location  in  the  tree.  The 


DURATION  AND  LIMIT  OF  GROWING-SEASON. 


7 


difference  between  the  longest  and  shortest  season  at  the  base  was  111  days, 
and  82  days  in  the  upper  location. 

That  other  and  extremely  local  and  individual  conditions  are  operative 
may  be  seen  from  the  data  given  in  Table  2,  in  which  tree  No.  10  is  recorded 
as  having  begun  growth  98  days  later  than  No.  1,  discussed  above,  although 
it  stands  not  more  than  30  meters  distant  from  it,  where  the  slope  begins 
to  fall  away  to  the  north  and  the  exposure  is  to  cool  northwest  winds.  Tree 
No.  6,  standing  within  4  meters  of  No.  10,  began  growth  in  1920  on  March 
19,  or  21  days  earlier  than  No.  1.  These  differences  are  among  trees  which 
have  cut  off  the  lower  branches,  are  above  20  years  old,  but  have  not  yet 
slackened  terminal  development.  When  young  trees,  such  as  Nos.  16,  17, 
18,  19,  20,  21,  22,  and  23,  are  considered,  it  was  found  that  growth  extends 
over  a  much  greater  part  of  the  year  and  that  not  many  weekly  records 
are  entirely  devoid  of  record  of  some  enlargement.  As  will  be  noted  below, 
these  young  trees  also  show  differences  under  apparently  equivalent  con¬ 
ditions.  The  diversity  of  behavior  noted  offers  some  features  in  contrast 
with  those  of  the  white  pine  (Pinus  strobus  L.)  as  recorded  by  Dr.  H.  P. 
Brown.1 


Table  2. — Seasonal  activities  of  several  trees  of  Pinus  radiata. 


Tree  No. 

Year. 

Beginning. 

Ending. 

Period  of  activity. 

6 

1920 

Mar.  19 

Aug.  24 

158  days. 

1922 

Jan.  24 

Aug.  25 

213  days. 

1923 

Jan.  19 

Sept.  1 

225  days. 

10 

1921 

May  4 

Sept.  19 

138  days. 

1922 

Feb.  15 

June  4 

19  days  after  decapitated  11  feet  above 

base  (see  No.  15). 

1923 

Feb.  10 

No  action. 

12 

1921 

July  28 

Sept.  23 

57  days. 

1922 

Apr.  20 

July  30 

101  days. 

13 

1922 

Jan.  25 

Sept.  1 

219  days;  standing  in  swamp. 

14 

1922 

Apr.  3 

Sept.  10 

160  days;  girdled  May  18. 

1923 

Feb.  8 

July  14 

156  days;  dead. 

15 

1922 

June  12 

23  days  after  being  decapitated  7  feet 

above  base  (see  No.  10). 

16 

1923 

Growth  not  limited  by  seasons;  girdled  2  meters  above  base  March  8; 

topped  May  22. 

17 

1923 

Growth  not  limited  by  seasons. 

18 

1923 

Growth  not  limited  by  seasons;  topped  March  8. 

19 

1923 

J  3J1.  3 

Defoliated  March  8. 

20 

1923 

Growth  not  limited  by  seasons. 

21 

1923 

Dec.  25 

Basal  section  killed  by  boiling  oil  June  22 ;  growth  ceased 

1922 

July  14 

22 

1923 

Feb.  18 

Aug.  13 

176  days. 

The  13  trees  noted  above  were  from  12  to  30  years  old.  Nos.  6,  10,  13, 
14,  15,  20,  21,  and  22  stood  on  the  top  of  an  old  dune-hill,  or  on  its  margin 
within  100  meters  of  each  other.  No.  12  grew  on  a  seaward- facing  slope  a 
few  kilometers  distant.  Nos.  16,  17,  and  18  were  nearly  identical  as  to  age 
and  stature,  and  stood  in  a  swampy,  sheltered  valley  a  few  meters  distant 
from  No.  22.  No.  19  was  midway  on  a  north-facing  slope. 


XH.  P.  Brown.  Growth  studies  in  forest  trees.  Botan.  Gazette,  59,  197-240.  1915. 


8 


DENDROGRAPHIC  MEASUREMENTS. 


The  periods  given  in  Table  2  indicate  the  time  over  which  the  trunks 
were  continuously,  or  almost  continuously,  in  a  state  of  enlargement,  the 
interruptions  being  clearly  due  to  excessive  transpiration  or  some  factor 
which  masked  but  did  not  inhibit  growth.  Brief  impulses  which  may  cause 
the  trunk  to  increase  for  a  few  days  may  occur  at  almost  any  time  during 
the  cooler  or  winter  months,  which,  however,  may  have  a  total  effect  of 
increasing  the  diameter  as  much  as  0.2  to  0.4  mm.  Thus,  tree  No.  6,  which 
showed  but  very  slight  aftergrowth  in  1920,  made  some  accretion  as  recorded 
on  three  of  the  five  weekly  slips  from  the  dendrograph  preceding  January 
1,  1923. 

The  tendency  to  continuous  growth  is  more  marked  in  younger  trees,  and 
is  illustrated  by  the  records  of  Nos.  16,  17,  18,  19,  20,  and  21.  The  first 
three  stood  in  moist  soil  in  a  sheltered  place,  No.  19  was  on  the  slope  nearby, 
while  Nos.  20  and  21  were  on  the  flattened  top  of  the  old  dune-hill  on  which 
the  laboratory  stands.  All  of  these  trees  were  active  at  the  time  the  den- 
drographs  were  installed,  the  last  week  in  October  1922,  and  nearly  all 
of  them  made  some  growth  every  week  during  the  winter  months,  except 
for  brief  periods  of  a  few  days,  when  enlargement  would  be  stopped  by 
low  temperatures. 

The  longest  stoppage  was  due  to  a  storm  late  in  January.  Nos.  16,  17, 
and  20  were  enlarging  when  the  observations  were  begun  in  the  last  week 
of  October  1922,  and  were  still  active  at  the  corresponding  time  in  1923. 
The  brief  pauses  noted  above  may  not  be  laid  to  seasonal  limits,  and  hence 
these  trees  may  be  said  to  grow  the  year  round,  except  as  interrupted  by 
inclement  weather. 

No.  22,  which  was  within  7  meters  of  No.  21,  showed  no  accretion  during 
November  and  December,  and  did  not  begin  enlargement  until  45  days 
later  and  until  several  days  after  the  end  of  a  period  of  low  temperature. 
To  the  casual  observer  the  difference  in  the  situation  of  the  two  trees  would 
not  be  discernible.  This  period  of  low  temperature  was  characterized  by 
maxima  between  67°  and  63°  F.,  and  of  minima  between  30  and  36, 
and  was  accompanied  by  a  total  rainfall  of  3  inches  in  17  days.  With  the 
cessation  of  the  storm,  growth  began  with  the  rising  temperatures  in  these 
five  young  trees,  10  days  later  in  No.  22,  7  days  later  in  No.  10,  2  days  later 
in  Nos.  6  and  14,  and  at  both  base  and  upper  part  of  the  trunk  of  No.  1.  It 
would  seem  probable  that  the  meteoric  factors  which  tend  to  delay  growth 
in  a  locality  will  be  operative  to  some  extent  on  all  trees  in  the  region.  It 
is  to  be  recalled,  however,  that  growth  is  always  under  the  control  of  a 
complex  of  which  the  three  chief  components  are  temperature,  stored  food- 
material,  and  water-supply.  The  individual  character  of  the  stored  food- 
supply  and  the  uneven  distribution  of  ground-water  may  be  determinative 
and  be  responsible  for  wide  differences  between  neighboring  trees. 

The  duration  of  the  growth-period  is  also  a  function  of  the  age  of  the 
individual.  Thus,  by  reference  to  Table  2  it  may  be  seen  that  growth  began 
earliest  and  lasted  longest  in  Nos.  16,  20,  and  22,  which  ranged  from  10  to 
15  years  of  age,  in  contrast  with  Nos.  1,  6,  10,  and  14,  which  ranged  from 
about  25  to  35  years  old. 


THICKNESS  OF  WOODY  LAYERS. 


9 


GROWTH  OF  ROOTS. 

It  has  already  been  pointed  out  that  the  tips  of  roots  may,  like  the  shoot 
terminals,  grow  at  almost  any  time  during  the  cooler  season.  The  correla¬ 
tion  between  such  action  and  the  thickening  of  the  older  and  larger  roots 
does  not  appear  to  be  any  closer  than  it  is  between  the  apices  and  the 
cambial  layers  in  the  trunks.  A  dendrographic  lever  set  was  placed  in  a 
small  excavation  2  meters  from  the  base  of  Monterey  pine  No.  1  on  January 
9,  1923,  where  it  could  be  kept  in  bearing  with  a  root  about  4  cm.  in  thick¬ 
ness.  No  change  in  diameter  was  detected  until  April  5,  when  a  steady 
increase  began,  which  continued  for  about  a  month,  with  a  total  accretion 
of  1  mm.  in  thickness.  The  daily  variations  were  very  small,  and  of  a  type 
slightly  different  from  those  of  the  trunk. 

The  daily  course  of  change  consisted  of  a  contraction  beginning  before 
midnight,  which  was  gradual  until  daybreak,  when  it  became  more  abrupt 
coincidentally  with  the  contraction  of  the  trunk.  Shortly  after  midday, 
and  not  later  than  2  p.m.,  expansion  began  which  continued  until  nearly 
midnight,  when  the  course  of  the  pen  was  reversed  and  shrinkage  ensued. 
The  amplitude  of  these  changes  was  much  less  than  that  of  young  stems 
of  the  same  size,  but  seemed  to  bear  something  of  the  same  ratio  to  the 
total  diameter  as  the  daily  changes  in  old  trunks. 

THICKNESS  OF  WOODY  LAYERS  AND  LENGTH  OF 

GROWING  SEASON  OF  No.  1 

The  general  features  of  the  varying  thickness  of  layers  of  wood  with 
respect  to  the  distance  from  the  base  of  the  trunk  are  presented  in  the 
accompanying  paper  by  Dr.  Shreve.  It  will  be  profitable,  however,  to 
present  the  results  derived  from  the  dendrographic  records  of  the  two  parts 
of  the  trunk  of  No.  1,  a  little  over  1  meter  from  the  base  and  8  meters 
higher. 


Table  3. — Annual  increases  in  thickness  and  length  of  growing- 

season  of  Monterey  pine  No.  1. 


Increases  in  diameter. 

Length  of  season  in  days. 

Year. 

A 

B 

A 

B 

mm. 

mm. 

1919 

8 

153 

1920 

10 

11 

184 

175 

1921 

26 

19 

264 

257 

1922 

19 

13 

221 

182 

1923 

8 

8.3 

236 

236 

A  cessation  of  growth  late  in  June  1920  being  associated  with  a  dry  con¬ 
dition  of  the  soil,  the  tree  was  copiously  irrigated,  as  already  described. 
The  growing-season  was  thus  lengthened  and  the  amount  of  wood  to  be 
attributed  to  the  renewed  growth  was  about  4  mm.  in  thickness,  as  con¬ 
firmed  by  samples  taken  with  the  increment  borer. 


10 


DENDROGRAPHIC  MEASUREMENTS. 


The  growing-season  thus  lengthened  artificially  and  the  longer  growing- 
season  of  1921  are  fairly  well  correlated  with  the  amounts  of  wood  formed 
in  each  year.  By  a  revised  estimate,  tree  No.  1  was  taken  to  be  36  years 
old  at  the  close  of  the  season  of  1923.  (This  is  in  correction  of  erroneous 
statement  made  in  “Growth  in  trees,”  Pub.  307,  1921,  p.  22.)  As  has  been 
previously  pointed  out,  this  tree  has  four  easily  identifiable  secondary  layers 
formed  in  late  summer,  accompanying  heavy  September  rainfall,  and  one 
as  a  result  of  the  irrigation  given  it  in  July  1920. 

The  measurements  given  by  Dr.  Shreve  in  a  separate  section  of  this  paper 
show  that  at  the  age  of  this  tree  the  zone  of  greatest  accretion  is  generally 
in  the  upper  half  of  the  trunk,  although  several  exceptions  were  noted. 

The  setting  of  the  dendrograph  was  changed  each  year  to  measure  a  new 
diameter,  and  one  which  might  be  a  few  centimeters  above  or  below  that 
of  the  previous  year. 

It  is  to  be  noted  further  that  in  checking  the  totals  calculated  from  the 
dendrographic  record  by  cores  secured  by  the  increment  borer,  such  samples 
are  usually  taken  a  few  centimeters  distant  from  the  radii  upon  which  the 
contacts  of  the  instrument  have  been  made,  and  more  exact  correspondence 
is  not  to  be  expected  between  the  totals  from  the  record  and  the  measure¬ 
ments  of  the  samples. 

SEASONAL  ACTIVITY  AND  WOOD-FORMATION  IN 

SEVERAL  MONTEREY  PINES. 

Monterey  pine  No.  6,  on  which  measurements  of  the  growth  of  1920  had 
been  previously  described,  was  a  tree  still  growing  vigorously  in  the  terminal 
shoot  and  at  the  close  of  1922  had  an  age  of  25  years  (20  by  an  earlier 
estimate) .  This  tree,  with  a  growing-period  of  158  days  in  1920,  had  made 
an  increase  of  8  mm.  in  diameter,  and  samples  taken  with  an  increment 
borer  showed  layers  3  mm.  in  thickness.  The  growing-period  in  1922  com¬ 
prised  243  days,  wfith  an  increase  of  10  mm.  in  diameter,  which  is  identical 
with  the  readings  of  a  sample  taken  near  one  of  the  points  of  contact. 

The  growing-season  of  1922  was  taken  to  be  closed  on  August  25.  Late 
in  November,  however,  the  slight  impulses  of  enlargement,  which  are  char¬ 
acteristic  of  the  species  in  this  region,  were  manifest,  with  repetitions  in 
December,  with  a  further  total  increase  of  0.7  or  0.8  mm.  in  thickness. 

The  growing-season  of  1923  opened  on  January  19,  and  may  be  taken  as 
terminating  on  September  1.  The  total  increase  in  diameter  during  the 
period  of  225  days  was  8  mm. 

Monterey  pine  No.  12  was  a  slowly  growing  tree  which  stood  on  a  sea¬ 
ward  slope  facing  southwest,  5  miles  from  the  Coastal  Laboratory.  It  had 
a  height  of  16  meters  and  a  diameter  of  22  cm.  at  the  place  of  attachment 
of  the  dendrograph.  The  growing-period  for  1.921  included  only  57  days, 
in  which  an  increase  of  1.5  mm.  in  diameter  was  made.  In  1922  the  grow¬ 
ing-period  was  of  nearly  double  length,  being  101  days,  in  which  an  increase 
of  less  than  1  mm.  was  made. 

Monterey  pine  No.  13  was  about  10  meters  in  height,  20  cm.  in  diameter, 
and  stood  in  the  swampy  portion  of  the  garden,  where  the  soil  at  all  times 
had  an  adequate  supply  of  moisture.  It  is  to  be  noted  that  the  length  of 


SEASONAL  ACTIVITY  AND  WOOD-FORMATION. 


11 


the  growing-season  for  this  tree,  however,  wTas  not  as  great  as  that  of  No.  6, 
which  stood  on  a  dry  slope.  The  layer  of  1922  in  a  sample  taken  near  the 
dendrograph  had  a  thickness  of  about  8  or  9  mm.  The  integration  of  the 
dendrographic  record  showed  a  gain  of  13.6  mm.  in  diameter,  which  would 
indicate  a  woody  layer  formed  under  the  dendrographic  bearings  of  lesser 
thickness  than  that  found  by  the  increment  borer.  This  tree  was  irregular 
in  form  and  stood  in  a  leaning  position.  It  forms  the  most  notable  example 
of  a  difference  between  the  dendrographic  record  and  direct  measurement 
of  cores  taken  from  the  trunk. 

Three  young  trees  standing  in  a  group  in  the  moist  soil  of  the  garden 
were  selected  for  observation  late  in  1922.  All  were  under  18  years  old,  with 
a  height  5  to  6  meters,  and  of  diameters  as  indicated  below.  Nos.  16  and  18 
were  used  as  experimental  subjects,  as  described  in  the  following  section 
of  this  paper,  and  No.  17  was  used  as  a  reference  or  control,  its  relations  to 
the  soil  not  being  altered  in  any  way,  nor  was  any  excision  of  branches 
practised.  The  trunk  at  a  distance  of  1.5  meters  from  the  base  had  a  diam¬ 
eter  of  16  cm.  and  showed  layers  in  a  sample  taken  by  the  increment  borer 
at  that  height  indicating  an  age  of  16  years  at  the  close  of  the  season  of 
1923.  Nearly  all  of  the  branches  were  still  present,  several  large  ones 
arising  from  the  trunk  below  the  dendrograph.  Those  of  the  upper  part  of 
the  trunk  were  still  leafy  to  the  base.  The  trunk  showed  a  thickening  and 
flaking  of  the  bark  in  the  basal  section  below  the  dendrograph,  but  above 
this  was  still  green  and  continuous. 

A  dendrograph  was  attached  October  23,  1922,  at  which  time  some  slight 
enlargement  was  in  progress.  Pauses  between  November  20  and  26,  and 
December  4  and  26,  were  noted.  Later  the  disturbance  which  affected  many 
other  trees  caused  this  tree  to  stop  growth  between  January  22  and  February 
7,  1923.  The  difference  between  the  activity  of  this  tree  and  that  of  No. 
16,  which  stood  within  3  meters  of  it  are  to  be  noted. 

The  trunk  of  No.  17  made  an  accretion  of  about  1.3  mm.  during  the 
October-November  period  of  activity.  An  enlargement  of  1  mm.  in  diam¬ 
eter  had  taken  place  when  growth  was  interrupted  between  January  22  and 
February  3  in  all  young  trees.  An  actual  shrinkage  occurring  during  this 
time,  which  amounted  to  about  1  mm.,  may  be  attributed  to  actual  water- 
loss  from  the  newly  formed  cells,  and  from  cortical  elements.  A  further 
growth  or  increase  in  the  diameter  of  19  mm.  had  taken  place  by  October  23, 
at  which  time  enlargement  was  still  in  progress.  It  may  be  inferred  that  the 
contraction  in  the  January-February  pause  was  taken  up  by  the  subsequent 
distention  of  the  cells  affected,  so  that  the  net  growth  to  October  23  may 
be  taken  as  20.5  mm.  This  was  in  fair  agreement  with  the  measurements 
of  layers  in  cores  taken  by  the  increment  borer,  although  it  was  seen  that 
some  increase  of  the  young  bark  would  be  included  in  the  dendrographic 
record.  The  bark  was  still  green  and  had  not  begun  to  form  flakes,  so  that 
the  bearings  were  taken  from  the  outer  surface.  Here,  as  in  No.  20,  two  or 
more  layers  of  wood  had  been  formed  every  year.  It  would  appear  that 
each  serious  interruption  of  growth  would  mark  the  limits  of  distinguishable 
layers  of  wood. 

The  record  of  Monterey  pine  No.  17,  as  given  above,  is  to  be  taken  as 
the  first  actual  observation  of  growth  in  trees  nearly  continuous  throughout 


12 


DENDROGRAPHIC  MEASUREMENTS. 


the  year.  It  is  highly  probable  that  the  duration  of  activity  described 
represents  nearly  the  maximum  duration  of  activity. 

Monterey  pine  No.  20  stood  on  the  level  ground  near  a  small  glass  house 
in  a  place  where  the  soil-moisture  was  somewhat  above  that  around  trees 
Nos.  21  and  22,  which  were  not  far  distant.  The  diameter  of  the  trunk  at 
a  distance  of  80  cm.  from  the  base  was  9.5  cm.  at  the  close  of  the  season  of 
1923,  while  the  height  to  the  top  of  the  leader  of  this  season  was  about  6 
meters.  Nearly  all  of  the  branches  were  still  present  and  all  except  those 
below  the  dendrograph  still  bore  leaves  clear  to  the  base.  Cores  taken 
below  the  dendrograph  showed  that  the  age  of  the  tree  was  about  12  years. 

The  instrument  was  put  in  place  on  October  25,  1922,  at  which  time 
enlargement  was  in  progress.  Pauses  were  noted  December  4  to  11,  and 
January  20  to  26,  1923,  which  was  much  shorter  than  that  of  No.  16  and 
No.  17,  which  were  in  a  swampy  situation  100  meters  distant.  Another 
pause  was  noted  between  March  30  and  April  10,  and  between  April  13  and 
16,  after  which  time  enlargement  was  continuous  and  still  in  progress  on 
the  anniversary  of  the  experiment.  The  total  increase  in  the  diameter  of 
the  trunk  during  the  year  was  19.5  mm.,  and  a  state  of  active  enlargement 
prevailed  all  of  the  year,  except  a  total  of  30  days. 

The  total  accretion  did  not  differ  widely  from  measurements  of  the  layers 
in  cores  taken  with  the  increment  borer.  It  is  to  be  noted  that  the  number 
of  layers  of  wood  as  distinguished  by  the  appearance  of  the  wood  was  more 
than  twice  that  of  the  actual  number  of  years  of  existence,  suggesting  that 
the  interruptions  in  growth,  which  have  been  noted  above,  would  be  denoted 
by  differences  which  would  give  the  appearance  of  additional  annual  layers. 
If  the  ages  of  the  young  trees  were  reckoned  from  the  number  of  layers,  a 
figure  would  be  obtained  which  would  be  more  than  double  that  of  the 
known  age. 

The  interruptions  to  enlargement  were  not  coincident  with  those  affecting 
No.  17  and  others.  A  pause,  not  directly  referable  to  the  weather,  in 
December  and  one  in  April  are  noted,  but  neither  of  them  might  be  taken 
as  a  seasonal  limit.  This  tree  would  be  coordinate  with  No.  17  in  establish¬ 
ing  a  record  for  growth  without  seasonal  limits. 

Monterey  pine  No.  22  was  a  sparingly  branched  tree  about  4.5  meters  in 
height,  with  all  of  the  lower  branches  cast  off  below  a  point  2  meters  from 
the  base.  The  diameter,  1  meter  from  the  base  at  the  place  in  which  den- 
drographic  bearings  were  made,  was  9  cm.  at  the  close  of  the  season  of  1923. 
An  estimate  made  on  the  layers  of  wood  in  a  core  taken  at  the  height  of  a 
meter  showed  that  the  tree  was  about  16  years  old  at  the  end  of  1923.  This 
tree  was,  therefore,  older  than  No.  20,  which  stood  within  75  meters  and 
under  conditions  apparently  similar,  although  long  familiarity  with  the  soil 
formation  leads  to  the  knowledge  that  its  soil-water  supply  was  less.  Still 
other  differences  in  the  two  trees  became  apparent  when  the  dendrographic 
record  for  1923  was  integrated. 

The  instrument  was  attached  on  October  25,  1922.  It  was  not  possible 
to  fix  upon  any  week  in  which  any  definite  or  irreversible  enlargement 
occurred,  but  an  increase  of  about  0.5  mm.  in  diameter  had  been  made  by 
the  end  of  December.  No  increase  whatever  was  discernible  in  the  following 
6  weeks,  but  an  enlargement  began  on  February  18  which  may  be  taken  as 


EXPERIMENTAL  INVESTIGATIONS. 


13 


the  beginning  of  the  seasonal  activity.  Growth  continued  at  varying  rates 
until  August  13,  a  total  period  of  176  days,  which  was  shorter  than  that  of 
the  period  of  growth  of  Nos.  16,  17,  and  20  by  more  than  100  days. 

The  total  increase  in  diameter  in  this  time  was  7  mm.,  which  is  in  accor¬ 
dance  with  the  measurements  of  the  recently  formed  layer  on  cores  taken  by 
the  increment  borer.  The  trunk  of  this  tree  was  seen  to  be  much  different 
from  that  of  No.  20,  notably  in  the  fact  that  but  one  layer  of  wood  is  formed 
annually,  while  in  No.  20  two  or  more  may  be  formed  in  every  year.  Plans 
were  therefore  made  to  continue  the  record  of  both  trees,  to  ascertain  to 
what  age  this  difference  in  activity  would  be  held. 

EXPERIMENTAL  INVESTIGATIONS. 

EFFECTS  OF  BREAKING  THE  CONDUCTING  SYSTEM  BY 

GIRDLING. 

Growth  is,  of  course,  closely  connected  with  the  translocation  of  material. 
Whatever  may  be  the  actuating  forces  which  drive  solutions  from  the  roots 
upward  and  organic  material  downward  through  the  stem,  it  is  clear  that 
this  takes  place  chiefly  in  the  layers  of  wood  which  have  been  formed  within 
the  last  two  or  three  years  of  the  life  of  the  tree.  Recent  contributions, 
particularly  those  of  Dixon,  lead  us  to  ascribe  a  minor  role  to  the  bast  or 
phloem  in  the  movements  of  material.  It  has  long  been  known,  however, 
that  the  removal  of  the  cortical  and  other  cell-masses,  including  the  bark, 
external  to  these  layers  caused  serious  interruptions  in  the  translocation 
streams,  although  the  wood  was  left  unaltered  except  by  the  inevitable 
desiccation  resulting  from  being  laid  bare.  Some  girdling  experiments,  with 
the  effects  on  growth  and  the  movements  of  material  are  described  in  the 
following  paragraphs. 

Monterey  pine  No.  14  stood  on  a  north-facing  slope  near  Nos.  6,  10, 
and  15.  Its  height  was  about  the  same  as  No.  6,  being  about  20  meters, 
and  the  trunk  had  a  diameter  of  20  cm.  at  the  place  of  attachment  of  the 
dendrograph.  Its  estimated  age  may  be  taken  to  be  about  22  years  at  the 
close  of  the  season  of  1923.  The  layer  on  a  sample  taken  near  the  attach¬ 
ment  of  the  dendrograph,  formed  in  1922,  was  not  much  over  2  mm.  in  thick¬ 
ness,  and  the  layers  made  in  the  two  previous  years  were  not  more  than 
double  this  amount.  The  integration  of  the  dendrographic  record  showed 
an  increase  of  slightly  less  than  5  mm.  in  diameter  during  the  time  in  which 
the  observations  were  made,  beginning  April  3.  Not  much  accretion  could 
have  been  made  before  this  date,  however.  Chief  interest  centers  in  the 
fact  that  a  belt  of  bark,  bast,  and  cambium  25  cm.  wide,  with  the  lower 
edge  40  cm.  above  the  base,  was  removed  on  May  18,  1922.  This  girdling 
does  not  appear  to  have  hastened  the  closure  of  the  growing-period.  The 
thickness  of  the  layer  of  wood  formed,  however,  was  less  than  that  in  any 
previous  year  (fig.  1). 

Growth  began  in  1923  on  February  8,  which  was  two  weeks  later  than 
No.  6,  standing  near  it  and  referred  to  as  a  control,  but  a  week  earlier  than 
No.  10,  the  crown  and  most  of  the  branches  of  which  had  been  removed  in 
the  previous  season  as  described  below.  Enlargement  of  the  trunk  con¬ 
tinued  until  about  March  1,  and  in  the  three  weeks  of  activity  an  increase 


14 


DENDROGRAPHIC  MEASUREMENTS. 


of  1.5  mm.  diameter  was  made.  The  daily  equalizing  variation,  which  had 
never  been  very  marked,  now  almost  disappeared,  the  pen  tracing  as  nearly 
a  straight  line  as  ever  occurs  in  such  records.  By  mid-June  the  leaves 
showed  a  distinct  yellow  tone,  which  was  most  marked  on  the  lower 
branches,  and  the  tree  appeared  to  be  dying. 

A  final  examination  of  the  trunk  on  June  28  showed  that  the  cambium 
was  dead  below  the  girdle  and  that  the  rays  were  practically  emptied  of 
starch.  Above  the  girdle  an  average  amount  of  starch  was  present  in  the 
dead  and  dying  tissues  for  a 
distance  of  about  a  meter 
above  the  girdle;  beyond  this 
the  rays  were  practically  empty 
for  a  distance  of  3  meters, 
which  was  examined  and  on 
which  only  short  dead  branches 
were  borne.  Just  at  this  time 
a  renewed  enlargement  of  the 
trunk  began  (June  27),  which 
continued  with  almost  no  daily 
variation  until  July  15,  when 
the  record  again  became  a  di¬ 
rect  line,  with  the  daily  equal¬ 
izing  variation  not  discernible. 

The  total  increase  calculated 
from  the  record  during  this 
second  period  was  about  1.2 
mm.  It  is  notable  that  the 
daily  variation  is  a  function  of 
living  trees,  even  when  meas¬ 
ured  on  the  inner  part  of  the 
trunk,  and  that  it  disappears 
from  dead  trunks  or  from  those 
which  have  been  decapitated 
or  defoliated. 

The  tree  was  felled  by  cut¬ 
ting  the  trunk  near  the  base  on 
July  25,  1923.  The  cambium 

was  all  dead  except  in  a  belt  of  p1G  j — Monterey  pine  No.  14,  girdled  in  May  1922. 
callus  above  the  girdle,  which 

was  only  a  few  centimeters  in  width.  This  seemed  to  comprise  all  of  the 
living  cells  in  the  tree,  as  the  branches  were  brittle  and  dry  and  the  root- 
system  was  completely  dead.  The  trunk,  however,  was  still  high  in  water- 
content.  No  starch  was  present  below  the  girdle,  and  above  the  residues 
were  sparsely  and  irregularly  distributed  in  the  medullary  rays  of  the 
extreme  outer  layers.  The  boring  beetle  which  inhabits  this  tree  was 
abundant  in  the  upper  part  of  the  trunk. 

The  tree  was  cut  into  short  sections  and  an  examination  of  the  layers 
of  wood  made  by  Dr.  Shreve.  The  thickness  of  the  layer  of  1923  at  differ¬ 
ent  distances  from  the  base  were  determined  as  follows: 


EXPERIMENTAL  INVESTIGATIONS. 


15 


Table  4. 


Distance 
from  base. 

Thickness 
of  layer 
formed  in 
1923. 

Distance 
from  base. 

Thickness 
of  layer 
formed  in 
1923. 

Distance 
from  base. 

Thickness 
of  layer 
formed  in 
1923. 

meters. 

mm. 

meters. 

mm. 

meters. 

mm. 

17 

0.8 

10 

1.2 

3 

1.0 

16 

0.7 

9 

1.3 

2 

0.8 

15 

0.9 

8 

1.1 

1 

2.3 

14 

1.0 

7 

1.5 

0.8 

1.0 

13 

1.0 

6 

0.9 

0.3  girdle;  no  wood  below. 

12 

1.7 

5 

1.0 

11 

1.4 

4 

1.2 

As  may  be  seen,  the  greatest  amount  of  wood  was  formed  in  the  zone 
immediately  above  the  girdle  and  under  the  dendrograph  in  which  part  the 
greatest  accumulation  and  residue  of  starch  was  also  found. 

The  second  experiment  in  girdling  was  made  on  a  tree  which  was  topped 
later  in  the  season.  A  small  tree,  No.  16  of  the  trio  which  stood  in  the  moist 
soil  of  the  garden  and  which  was  very  similar  to  No.  17,  showed  a  diameter 
of  over  15  cm.  at  1.5  meters  above  the  base,  near  the  point  at  which  the 
dendrograph  was  attached.  The  tree  retained  nearly  all  of  its  branches, 
the  lowermost  touching  the  ground,  and  nearly  all  were  leafy  to  the  base. 
A  half  dozen  of  the  largest  arose  from  the  trunk  below  the  dendrograph, 
and  the  trunk  in  this  part  was  beginning  to  show  splitting  and  flaking  of 
the  bark.  The  dendrograph  was  attached  on  October  23,  1922,  at  which 
time  the  tree  was  in  a  growing  condition.  The  dendrograph  slip  was  not 
perfectly  adjusted  every  week,  but  it  was  evident  that  the  tree  made  some 
increase  every  week  and  that  no  actual  cessations  of  enlargement  could  be 
noted,  except  between  December  8  and  14,  1922,  January  20  and  27,  1923, 
and  January  29  and  February  7,  1923.  In  addition  to  these  disturbances, 
which  may  be  assigned  to  low  temperatures  accompanying  storms,  the  bark 
and  phloem  were  removed  in  a  zone  25  cm.  in  width  at  a  distance  of  0.5 
meter  above  the  dendrograph  and  above  a  very  vigorous  wThorl  of  large 
branches,  on  March  8,  with  the  result  that  both  growth  and  the  daily  varia¬ 
tion  were  reduced  to  a  minimum  for  10  days.  The  tree  was,  therefore,  in  a 
condition  of  measurable  growth  for  all  of  the  year,  except  35  days.  Three 
pauses  due  to  the  influence  of  storms  are  noted  and  one  to  the  effects  of 
girdling.  It  is  to  be  seen  that  the  tree  had  made  an  increase  of  18  mm.  in 
diameter,  which  is  to  be  compared  with  that  of  No.  17  in  the  same  period. 

A  zone  of  bark  cambium  and  cortex  15  cm.  wide,  the  lower  margin  of 
which  was  40  cm.  above  the  instrument,  was  removed  on  March  8.  Growth 
ceased  within  24  hours,  and  the  daily  variation  which  had  caused  the  pen 
to  move  up  and  down  2  or  3  mm.  on  the  chart  diminished  so  that  the  record 
was  now  a  direct  line.  This  inactivity  continued  until  March  19,  when 
some  variation  was  noticeable,  and  actual  enlargement  began  on  the  23rd, 
and  the  growth  which  followed  made  a  dendrographic  record  in  which  no 
unusual  features  were  discernible. 


16 


DENDROGRAPHIC  MEASUREMENTS. 


A  second  modification  was  now  made.  The  main  stem  was  cut  off  1.5 
meters  above  the  dendrograph  on  May  22.  The  top  removed  was  about  5 
meters  long  and  weighed  50  kg.,  and  was  estimated  to  carry  about  half  the 
leaves.  The  part  of  the  tree  remaining  was  3  meters  in  height,  and  had 
been  girdled  a  meter  above  the  dendrograph  as  noted  above.  This  length 
bore  several  large  branches.  Growth  wras  not  noticeably  affected  by  the 
topping,  and  the  increase  which  took  place  afterward  and  up  to  the  middle 
of  September  amounted  to  13.5  mm.  increase  in  the  diameter.  It  is  to  be 
seen  that  this  tree  had  made  an  increase  in  diameter  of  18  mm.  in  the  same 
period  in  which  No.  17  had  made  an  increase  of  20.5  mm.  Girdling  and 
topping  had  apparently  had  no  direct  effect,  except  the  stoppage  of  growth 
for  a  few  days  as  described.  Other  experiments  in  topping  are  described 
elsewhere. 

The  cores  taken  by  the  increment  borer  show  three  layers  in  the  8  to  9 
mm.  thickness  of  wood  which  may  have  been  formed  in  the  period  under 
discussion.  The  outermost  was  not  over  2  mm.  thick.  The  bark  of  this  tree 
was  green  under  the  dendrographic  bearings,  which  were  made  on  its  outer 
surface,  and  some  thickening  may  have  taken  place  which  would  be  included 
in  the  record.  This  outermost  layer  and  some  bark  may  have  been  formed 
after  the  girdling,  which  was  done  in  March. 

An  examination  of  a  core  taken  from  the  girdled  zone  showed  that  a 
callus  had  been  formed  on  its  surface,  which  probably  accounts  for  the 
resumption  of  growth.  Beneath  this  were  two  layers  each  about  2  mm.  in 
thickness.  The  outermost  was  taken  to  represent  the  wood  formed  from 
about  the  time  of  the  beginning  of  the  observations  and  the  girdling  in 
March,  as  the  total  increase  in  diameter  during  that  period  had  been  4  mm. 
What  causes  delimited  a  period  in  which  the  layer  underneath  was  formed 
can  not  be  conjectured.  This  layer,  however,  is  present  in  other  parts  of 
the  trunk. 

It  is  evident  that  in  this  tree,  as  well  as  in  other  young  trees  of  the  species, 
the  formation  of  two  or  three  layers  of  wood  each  year  is  a  common  phe¬ 
nomenon.  These  layers  might  be  mistaken  for  annual  layers  when  cut 
from  the  core  of  an  older  tree.  Indeed,  their  appearance  in  the  younger 
tree  does  not  differentiate  them.  The  age  of  the  young  trees  being  known 
by  direct  observation,  and  the  yearly  accretion  determined  dendrographic- 
ally,  the  case  is  quite  clear.  The  causes  which  are  responsible  for  this 
multiplication  of  layers  in  this  tree  may  be  operative  in  tropical  trees,  in 
which  also  the  conditions  for  growth  are  favorable  during  almost  the  entire 
year. 

The  effects  of  basal  girdling  were  tested  upon  a  tree  still  smaller, 
Monterey  pine  No.  21.  This  tree  had  a  thickness  of  6  to  7  cm.  at  the 
base,  being  somewhat  irregularly  cylindrical.  Its  height  was  about  6  meters 
and  its  age  about  15  or  16  years.  Some  of  the  lowermost  branches  had 
been  lost,  but  most  of  the  upper  ones  were  still  leafy  to  the  base.  It  was 
enmeshed  with  the  branches  of  a  small  tree  of  Quercus  agrifolia,  which 
afforded  it  mechanical  support,  and  also  cut  its  illumination  somewhat. 

The  dendrograph  was  attached  October  28,  1922,  and  it  was  soon  seen 
that  a  slow  enlargement  was  in  progress.  This  ceased  on  December  11,  and 
was  not  resumed  until  December  25,  which  latter  date  may  be  taken  as  the 


EXPERIMENTAL  INVESTIGATIONS. 


17 


beginning  of  the  season  of  1923.  This  late  autumnal  growth  had  resulted 
in  an  accretion  of  about  1.5  mm.  in  diameter.  An  additional  2  mm.  laid 
on  before  the  pause  due  to  low  temperature  came  as  an  effect  of  the  storm 
late  in  January.  This  was  not  quite  as  marked  as  in  the  other  young  trees, 
as  cessation  of  growth  did  not  take  place  until  January  29,  and  began  again 
on  February  6.  A  further  increase  of  7  mm.  in  the  diameter  had  occurred 
when  the  base  of  the  stem  was  killed  on  June  22.  The  layer  of  wood  of  the 
implied  thickness  was  recognizable  in  a  core  taken  by  the  increment  borer. 
It  was  seen  that  more  than  one  layer  had  been  formed  every  year,  but  the 
limits  of  these  were  not  so  definitely  marked  as  in  Nos.  16,  17,  18,  and  20. 
Enlargement  continued  until  July  12,  in  which  an  additional  0.8  mm.  was 
added  to  the  woody  layer. 

Killing  of  a  basal  section  was  accomplished  as  follows:  A  sheet  of  thin 
lead  was  cut  to  form  a  truncated  cone  when  placed  around  the  tree.  A 
length  of  adhesive  tape,  such  as  is  used  for  making  insulation  in  electrical 
wiring,  was  wound  around  the  stem  at  a  distance  of  20  cm.  from  the  base 
to  afford  a  bottom  and  a  support  to  the  cone.  The  margins  of  the  sheet 
lead  having  been  fitted  with  holes  that  registered,  the  sheet  was  curved 
around  the  tree,  and  the  edges  brought  tightly  together  by  means  of  small 
bolts  and  two  strips  of  iron,  one  on  the  inner  and  one  on  the  outer  side  of 
the  junction.  The  small  end  of  the  inclosing  lead  cone  was  wired  tightly 
against  the  belt  of  tape  and  some  Canada  balsam,  made  thin  with  cedar 
oil,  was  poured  in  to  secure  the  seal. 

Two  liters  of  olive  oil  were  now  heated  to  110°  C.  and  poured  into  the 
cone,  immersing  a  length  of  20  cm.  of  the  stem.  A  small  immersion  electric 
heater  was  thrust  into  the  oil,  and  while  an  effort  was  made  to  keep  the 
entire  mass  of  oil  at  a  uniform  temperature  by  stirring,  yet  that  at  the 
lower  small  end  of  the  cone  remained  below  100°,  while  the  upper  half  was 
successfully  maintained  at  100°  C.  or  over  for  21/o  hours,  beginning  at 
lh30m  p.m.  on  June  22,  1923. 

The  temperature  of  the  stem  16  cm.  above  the  surface  of  the  oil  was 
48°  C.  at  4  p.m.,  and  24°  C.  at  45  cm.  above.  At  5  p.m.  the  temperature 
at  the  lower  position  had  fallen  to  40°  C.,  that  at  the  upper  to  24°  C., 
while  the  reading  of  the  thermometer  at  the  same  level  as  the  dendrograph 
was  16°  C.  It  may  be  inferred  that  the  temperature  of  the  cambium  layer 
under  the  dendrographic  bearings  was  not  raised  more  than  5°  by  the  use 
of  the  boiling  oil  on  the  zone  lower  down.  Such  a  slight  rise  probably 
accelerated  growth  temporarily.  That  the  entire  cross-section  of  the  stem 
was  killed  in  the  treated  zone  may  be  safely  inferred  from  the  results  of 
similar  treatment  of  tree  No.  24,  described  below. 

When  growth  ceased  on  July  12  a  period  of  five  days  followed  in  which 
the  daily  equalizing  variations  showed  unchanged  dimensions;  then  a  con¬ 
traction  began,  accompanied  by  a  diminution  of  the  daily  variations.  The 
diameter  decreased  2  mm.  in  a  week.  The  soil  about  the  roots  was  now 
irrigated  copiously  on  three  successive  days,  but  no  increase  in  diameter 
resulted.  This  implied  that  water  was  entering  the  root-system  in  increased 
quantity  and  the  root-system  was  undamaged,  but  that  the  amount  passing 
the  treated  zone  was  not  increased.  The  condition  of  this  part  of  the  trunk 
may  be  inferred  from  the  results  of  a  similar  treatment  of  another  tree 
(No.  24)  of  similar  size. 


18 


DENDROGRAPHIC  MEASUREMENTS. 


An  examination  of  the  effects  of  the  treatment  of  the  stem  with  boiling 
oil  was  made  on  Monterey  pine  No.  24.  This  tree  was  in  a  condition  of 
vigorous  growth  and  was  comparable  in  every  way  with  No.  21,  the  stem 
being  6  cm.  in  thickness.  A  fitting  of  a  truncated  and  inverted  cone  of  sheet 
lead  was  made  around  the  base,  duplicating  the  arrangement  described  for 
No.  21,  on  July  7,  1923.  This  was  filled  with  boiling  corn  oil  and  olive  oil 
from  lh30m  p.m.  until  4  p.m.  During  this  time  the  temperature  of  the  oil 
was  kept  between  100°  and  110°  C.  by  means  of  an  immersion  electrical 
heater;  48  hours  later  the  tree  was  cut  down  and  a  section,  including 
the  treated  zone,  examined.  The  outer  corky  bark  remained  intact,  the 
chlorophyll  was  destroyed  in  a  zone  23  cm.  wide,  and  a  zone  of  dead 
cambium  22  to  23  cm.  wide  was  found  beneath.  The  cortex  was,  of  course, 
destroyed,  as  well  as  the  rays.  Starch,  as  is  usual  with  these  trees,  was 
found  almost  wholly  in  the  rays  of  the  layer  of  wood  formed  in  the  previous 
year  in  addition  to  the  current  formation.  Its  presence  was  noted  when  the 
cells  were  treated  with  an  iodine  solution  which  accentuated  the  clumped 
condition  of  the  protoplasm. 

No  alteration  by  heat  could  be  detected  in  the  wood-cells  by  direct  obser¬ 
vation  with  low  magnification.  When  the  killed  section  was  split  length¬ 
wise  it  was  noted  that  the  wood  was  less  moist  to  the  touch  than  that 
immediately  above  and  below  the  treated  zone.  A  cross-section  in  the  form 
of  a  disk  was  made  20  cm.  below  the  treated  zone,  another  an  equal  distance 
above,  and  one  was  taken  from  the  middle  of  the  treated  zone  and  placed 
in  an  oven  at  70°  to  80°  C.  for  48  hours.  After  drying  for  48  hours  the 
sections  were  weighed  to  ascertain  the  loss  in  weight.  The  trunk  below  the 
girdle  had  evidently  lost  none  of  its  water  as  a  result  of  the  application  of 
the  boiling  oil,  as  two  samples  in  this  region  showed  a  water  content  which 
was  driven  off  in  the  drying  of  59  and  61  per  cent.  The  outer  wood  of  the 
upper  portion  of  the  treated  area  had  lost  much  of  its  water  by  the  treat¬ 
ment,  as  its  weight  was  reduced  by  only  31  per  cent  in  the  oven.  A  sample 
at  the  extreme  upper  margin  had  a  water  content  of  but  25  per  cent.  It  was 
evident  that  water  did  not  pass  freely  through  the  zone  killed  by  the 
heated  oil. 

The  contraction  of  the  stem  of  No.  21  recorded  by  the  dendrograph  may 
have  been  due  to  the  death  of  the  cambium  layer  under  the  bearings,  or  to 
the  loss  of  water  from  the  stem,  in  which  the  column  may  have  been  broken 
by  the  heated  oil.  In  order  to  ascertain  the  effects  of  an  increased  supply 
to  the  shoot,  five  of  the  six  branches  which  were  borne  on  the  young  trunk 
on  the  part  between  the  dendrograph  and  the  treated  section  below  were 
cut  off  and  the  stumps  immersed  in  flasks  of  w'ater  on  July  30  at  10  a.m. 
The  lowermost,  which  arose  a  few  centimeters  above  the  treated  zone,  was 
dipped  in  a  flask  of  Fuchsin  S,  1  part  in  1,000.  The  course  of  the  dye  in  this 
branch  was  traced,  with  the  idea  that  it  would  be  similar  to  that  of  the 
stream  of  water  taken  up  by  the  other  branches. 

At  1  p.m.  100  c.  c.  of  water  was  necessary  to  replace  the  liquid  which  had 
been  taken  from  the  flasks  of  water  and  dye  by  the  branches  which  dipped 
into  them.  Nineteen  hours  later,  at  8  a.m.  on  July  31,  325  c.  c.  of  water 
was  necessary  to  replace  the  amounts  withdrawn  from  the  flasks,  including 
the  one  containing  Fuchsin.  A  slight  upward  movement  of  the  pen  was 


EXPERIMENTAL  INVESTIGATIONS. 


19 


discernible.  The  morning  was  foggy,  and  the  day  continued  to  be  so,  with 
the  result  that  the  total  absorption  on  the  following  morning  was  but  225 
c.  c.,  and  that  day  being  overcast,  the  total  on  the  next  morning  was  but 
175  c.  c.  August  2  being  clear  and  warm,  the  absorption  on  the  morning 
of  the  3d  amounted  to  325  c.  c.  for  the  previous  24  hours.  The  absorption 
in  the  27  hours  ending  at  noon  on  the  4th  was  250  c.  c.,  a  portion  of  this 
period  being  foggy. 

The  absorption  in  the  21%  hours  ending  9h30m  on  the  5th  was  200  c.  c., 
the  afternoon  of  the  4th  being  warm  and  clear,  although  it  was  overcast  on 
the  forenoon  of  this  day. 

Absorption  for  the  23%  hours  ending  at  9  a.m.  on  the  6th  was  200  c.  c., 
the  day  being  overcast  and  the  morning  cool. 

Absorption  for  the  24  hours  ending  at  9  a.m.  on  the  7th  was  200  c.  c.,  it 
being  clear  in  the  afternoon  of  the  preceding  day,  but  cloudy  in  this  fore¬ 
noon. 

Absorption  for  the  day  ending  at  9  a.m.  on  the  8th  was  but  190  c.  c.; 
foggy  and  overcast. 

Absorption  in  the  24  hours  ending  at  9  a.m.  on  the  9th  was  200  c.  c.  A 
small  branch,  the  daily  absorption  of  which  was  on  the  average  25  c.  c.,  was 
refitted  to  a  water-system  suitable  for  applying  pressure,  after  the  end  had 
been  freshly  cut.  At  the  beginning  the  water  column  applied  to  the  end  of 
the  branch  had  a  pressure  of  about  1.4  cm.  of  water. 

The  total  absorption  at  9  a.m.  on  the  morning  of  the  10th  was  190  c.  c., 
of  which  but  17  c.  c.  had  gone  in  through  the  branch  fitted  with  the  pressure 
apparatus.  The  vertical  extension-tube  of  this  apparatus  was  now  filled 
with  mercury,  so  that  a  pressure  of  1.7  meters  of  mercury  was  exerted  on 
the  end  of  the  branch.  The  day  had  been  overcast  and  was  damp,  with  no 
sun  on  this  morning. 

Total  absorption  of  the  five  branches  dipped  in  open  flasks  was  175  c.  c., 
while  that  of  the  branch  with  pressure  applied  was  about  50  c.  c.,  or  double 
its  usual  amount,  bringing  the  total  absorption  by  the  tree  up  to  225  c.  c., 
as  measured  on  August  11. 

Total  absorption  of  the  five  free  branches  was  160  c.  c.;  that  of  the  one 
under  pressure  was  47  in  the  24  hours  ending  August  12  at  9  a.m.,  the  sky 
being  foggy  and  overcast. 

The  above  rate  of  absorption  of  water  continued  until  August  16,  at 
which  time  it  was  apparent  that  the  trunk  had  regained  about  one-fourth 
of  the  loss  by  contraction  following  the  cessation  of  growth.  The  amount 
of  water  taken  in  daily  now  showed  a  decrease  day  by  day,  so  that  but 
160  c.  c.  was  taken  in  during  the  first  15  days  of  September.  The  tree  was 
taken  down  October  1,  at  which  time  a  further  intake  of  120  c.  c.  had 
occurred.  The  total  amount  which  had  been  taken  through  the  ends  of  the 
branches  was  not  as  much  as  5  liters,  which,  of  course,  was  much  less  than 
the  actual  transpiration  of  the  tree  during  the  two  months  in  which  the 
ends  had  been  dipped  in  water. 

The  tree  showed  a  progressive  dying  and  desiccation  of  the  leaves  from 
the  lowermost  branches  upward,  so  that  at  the  end  of  September  green 
leaves  were  seen  on  the  branches  of  the  upper  half  of  the  tree  and  only  at 
the  ends  of  the  branches,  denoting  that  it  was  only  leaves  formed  during 


20 


DENDROGRAPHIC  MEASUREMENTS. 


the  present  year  which  were  still  alive.  The  tree  was  now  taken  down  for 
examination  and  dissection.  The  young  trunk  was  dry  to  the  touch  in  the 
vicinity  of  the  killed  region,  but  the  percentage  of  moisture  appeared  to 
increase  toward  the  top  and  also  below  the  treated  part.  The  leaves  were 
of  a  yellowish  tinge  and  it  was  obvious  that  the  whole  tree  was  approaching 
death. 

The  three  cases  of  girdling  described  above  represent  the  effects  of  three 
different  sets  of  experimental  conditions.  The  removal  of  the  bark  and 
phloem  from  a  basal  section  of  the  Monterey  pine  is  a  type  of  classical 
operation  which  has  been  practised  by  many  workers  and  a  wide  variety 
of  results  have  been  secured.  Girdling  in  this  manner  is  used  to  deaden 
trees  preliminary  to  burning  in  the  clearing  of  forest  lands.  This  treatment 
presumably  does  very  little  direct  damage  to  the  rays  and  the  wood-cells. 
If  cells  capable  of  division  remain,  a  callus  may  be  formed  and  the  tree  may 
resume  growth.  This  usually  takes  place  in  many  young  trees,  and  in  some 
species  at  any  age. 

A  second  feature  which  may  affect  the  result  of  the  girdling  is  the  pres¬ 
ence  of  vessels  and  elongated  conduits  in  the  stem,  along  which  liquids  might 
move  with  speed.  Such  conduits  are  lacking  in  the  pine,  in  which,  however, 
the  perforations  in  the  membranes  of  the  bordered  pits  offer  a  passage  for 
minute  particles  as  described  by  Bailey.1 

Girdling  in  the  above  manner  is  followed  by  results  in  this  tree  which  are 
in  fair  agreement  with  those  recently  described  by  0.  F.  Curtis,  who  experi¬ 
mented  with  Prunus,  Cornus,  Pyrus,  Acer,  Syringa,  and  Ligustrum.  The 
increase  of  carbohydrates  in  the  zone  above  the  girdle  and  in  the  weight  or 
thickness  of  the  bark  found  by  Curtis  is  in  agreement  with  the  starch  above 
the  girdle  and  continued  growth  in  that  zone.  Curtis  finds  lessened  tran¬ 
spiration  in  girdled  trees.2 

The  death  and  desiccation  of  the  basal  part  of  the  tree  and  death  setting 
in  at  the  tip  of  the  shoot  is  a  distinctive  feature  in  the  Monterey  pine. 
Girdling  higher  up  in  a  young  tree  checked  growth  below  for  a  short  time, 
but  it  was  renewed  with  the  formation  of  a  callus  over  the  girdle. 

The  severer  treatment,  by  which  the  entire  stem  was  subjected  to  a  high 
temperature  which  would  kill  all  cells  and  alter  the  condition  of  the  walls, 
though  not  visible,  resulted  in  the  speedy  cessation  of  growth  above  the 
girdle  and  a  gradual  desiccation  and  death  of  leaves  from  below  upward. 

**  ^Branches  above  the  girdle  soon  lost  capacity  for  taking  in  water  through 
their  cut  ends.  Killing  and  girdling  may  disrupt  or  disturb  the  passage  of 
water  upward,  and  the  diffusion  of  electrolytes  principally  in  the  same 
direction  and  the  movements  of  organic  material  with  large  molecular  par¬ 
ticles  in  both  directions.  That  any  phase  of  such  transfers  takes  place 
exclusively  through  the  phloem  is  by  no  means  clear.  That  the  phloem  can 
not  be  destroyed  or  removed  without  some  disturbance  is  equally  clear.  It 
is  also  true  that  in  addition  to  the  electrolytes,  carbohydrates  and  proteins 
are  found  in  the  woody  tracts.  The  tests  with  Fuchsin,  described  in  another 

1I.  W.  Bailey.  The  structure  of  the  bordered  pits  of  conifers  and  its  bearing  upon  the  tension 
hypothesis  of  the  ascent  of  sap  in  plants.  Botan.  Gazette,  62,  133-142.  1916. 

2  O.  F.  Curtis,  The  effect  of  ringing  a  stem  on  the  upward  transfer  of  nitrogen  and  ash 
constituents.  Amer.  Jour.  Bot.,  10,  361.  1923. 


EXPERIMENTAL  INVESTIGATIONS. 


21 


section  of  this  paper,  show  that  colloidal  material  with  large  colloidal  par¬ 
ticles  may  move  freely  through  wood  in  either  direction,  but  that  this  move¬ 
ment  is  much  greater  in  some  parts  of  the  recently  formed  layers  than  in 
others.  That  such  differentiation  is  identical  in  different  trees  is  not 
probable.1  It  is  suggested  that  the  difference  in  the  conducting  capacity 
of  the  separate  layers  of  wood  may  rest  upon  the  condition  of  the  mem¬ 
branes  of  the  bordered  pits  and  upon  the  size  of  the  perforations.  Both 
might  be  altered  by  the  treatments  described  above.  Direct  measurement 
of  the  perforations  in  the  Monterey  pine  and  of  changes  which  may  be  pro¬ 
duced  by  experimental  methods  will  be  necessary  for  any  further  progress 
in  the  solution  of  this  problem.  It  is  to  be  seen  that  the  ascent  of  sap  and 
the  movement  of  material  in  dicotyledonous  stems  with  vessels  of  relatively 
large  caliber,  and  in  conifers  where  the  free  passages  are  minute  perfora¬ 
tions  in  thin  elastic  membranes,  deals  with  a  wide  range  of  surface  tensions. 

REDUCTION  OF  TOTAL  CAPACITY  OF  GREEN  LEAVES 

BY  TOPPING. 

One  experiment  has  already  been  described  by  which  a  part  of  the  stem 
and  the  upper  branches  were  removed  without  immediate  effect  on  the 
growth.  This  was  in  a  tree  in  which  the  branches  were  numerous  and 
densely  leaved.  Such  an  operation,  of  course,  lessens  the  transpiring 
surface  and  also  photosynthetic  capacity  of  the  tree.  One  experiment  was 
carried  out  in  which  the  branches  and  leaf  surfaces  were  removed  entirely, 
and  as  but  little  water  would  be  evaporated  from  the  cut  surface  of  the 
trunk  or  through  the  bark,  the  movement  of  material  upward  must  have 
been  stopped,  while  the  supply  of  soluble  material  which  could  move  down¬ 
ward  was,  of  course,  cut  off. 

The  trunk  of  Monterey  pine  No.  15  was  cut  away  at  a  height  of  2.2 
meters  from  the  base  on  May  18,  1922.  The  trunk  had  a  diameter  of  12 
cm.  and  was  about  20  years  old,  being  referable  to  No.  6  as  a  control.  A 
dendrograph  had  been  put  in  place  a  few  days  previously,  its  contacts 
being  about  50  cm.  below  the  cut,  and  the  trunk  was  found  to  be  in  a  state 
of  vigorous  enlargement.  No  branches  remained  on  the  trunk  after  the 
operation  (see  fig.  2).  Enlargement  continued  for  19  days,  during  which 
time  an  increase  of  0.6  mm.  in  diameter  was  made.  The  core  made  by  an 
increment  borer  showed  that  the  total  addition  to  the  wood  during  the 
season  varied  between  2  and  3  mm.  in  different  places. 

An  examination  at  the  end  of  the  season,  in  October,  showed  that  the 
wood  was  light  in  weight,  but  an  abundance  of  starch  and  other  material 
was  still  to  be  seen  in  the  rays  and  thin-walled  cells.  Some  shrinkage  fol¬ 
lowed  the  cessation  of  growth.  The  bast  and  cambium  were  found  to  be 
dead  in  a  length  of  6  cm.  in  the  terminal  portion  of  the  stem  on  July  28, 
over  2  months  after  decapitation. 

The  presence  of  the  food-material  suggests  that  inactivity  and  death  was 
not  due  directly  to  the  lack  of  building  material.  The  decapitation  would 
cut  off  the  supply  of  products  of  the  activities  of  leaves  and  these  may  have 

1 1.  W.  Bailey.  The  structure  of  the  bordered  pits  of  conifers  and  its  bearing  upon  the  tension 
hypothesis  of  the  ascent  of  sap  in  plants.  Botan.  Gazette,  62,  133.  1916. 


22 


DENDROGRAPHIC  MEASUREMENTS. 


included  substances  which  activated  the  enzymes.  Their  absence  made  the 
starch  present  unavailable  to  the  growing  cells.  The  upward  movement  of 
material  from  the  roots  would,  of  course,  be  stopped,  but  the  failure  of  the 
supply  of  some  unknown  substance  formed  in  the  leaves  and  translocated 
directly  down  the  stem  would  be  a  theoretical  explanation  of  the  stoppage 
of  growth. 


Fig.  2. — Monterey  pine  No.  15,  the  trunk  of 
which  was  cut  2  meters  above  base  in 
May  1922. 

Fig.  3. — Monterey  pine  No.  10,  the  trunk  of 
which  was  cut  a  few  meters  from  base 
and  above  some  small  branches. 


Fig.  2. 


Fig.  3 


EXPERIMENTAL  INVESTIGATIONS. 


23 


The  behavior  of  such  trees  as  Sequoia  and  other  kinds  in  which  the 
removal  of  all  or  part  of  the  trunk  causes  buds  to  start  on  the  roots  or  the 
stump  must  be  taken  to  indicate  the  presence  of  such  an  activating  or 
unlocking  substance  in  all  parts  of  the  plant  at  all  times.  That  the  activity 
of  the  full  crown  of  the  tree  may  be  necessary  to  furnish  a  supply  of  this 
material  in  the  Monterey  pine  is  suggested  by  the  behavior  of  the  trees 
when  nearly  all  of  the  branches  and  leaves  are  removed,  as  was  done  with 
Monterey  pine  No.  10. 

The  trunk  of  this  tree  was  cut  squarely  across  at  a  point  3  meters  from 
the  base  on  May  15,  1922.  The  trunk  was  13  cm.  in  diameter  at  the  point 
at  which  the  dendrograph  was  attached  in  1922.  The  tree  stood  on  a  north¬ 
facing  slope,  with  a  scanty  soil-moisture  supply,  and  appeared  to  form  but 
one  layer  of  wood  annually.  The  estimate  of  age  based  on  the  count  of 
the  layers  in  a  core  taken  by  the  increment  borer  made  the  tree  to  be  25 
years  old  at  the  end  of  1923. 

Growth  was  measured  continuously  from  February  28,  1921.  The  layer 
of  wood  formed  in  1921  was  3  to  4  mm.  in  thickness  in  samples  taken  by 
the  increment  borer,  and  the  dendrographic  record  for  that  year  at  a  point 
1.25  meters  above  the  base  showed  an  increase  of  7  mm.  with  a  growing 
period  of  138  days. 

This  tree  stood  on  a  north-facing  slope  and  is  referable  to  No.  6  as  a 
control,  being  under  much  the  same  conditions  as  No.  14  also. 

Enlargement  began  on  February  15  in  1922,  as  compared  with  a  begin¬ 
ning  date  of  May  4  in  the  previous  year.  It  was,  therefore,  well  in  the 
middle  of  a  vigorous  growing-season  when  it  was  decapitated  on  May  15, 
1922.  The  trunk  was  cut  squarely  across  at  a  point  about  3  meters  from 
the  base.  Five  small  branches,  with  an  average  length  of  a  meter,  arose 
from  the  terminal  30  cm.  of  the  stump.  Below  this  was  a  larger  and  heavier 
branch,  and  below  this  a  smaller  branch,  all  within  70  cm.  of  the  end  of  the 
stump.  (Fig.  3.) 

The  daily  contraction  did  not  take  place  on  the  day  following  the 
removal  of  the  top,  and  this  feature  of  behavior  was  not  noticeable  to  any 
degree  until  2  months  later,  some  fluctuation  showing  again  in  the  records 
early  in  August.  Enlargement  at  a  diminishing  rate  showed  during  the 
following  18  days,  when  it  ceased.  The  total  accretion  for  the  season,  which 
lasted  for  a  period  of  108  days,  amounted  to  5  mm.,  of  which  0.5  mm.  was 
after  topping.  The  cambial  layer  remained  alive  to  within  1  mm.  of  the 
cut  surface,  according  to  the  results  of  an  examination  made  in  mid-July. 
Four  of  the  five  smaller  branches  near  the  stump  died  in  1922,  but  three 
remained  alive  and  carried  green  leaves  in  the  following  year. 

Growth  began  on  February  10,  1923,  coincidentally  with  that  of  the 
control.  The  increase  was  exceedingly  slow  and  uncertain,  with  but  very 
slight  daily  fluctuations.  The  enlargement  became  definite  about  mid- 
June,  at  which  time  a  total  increase  in  diameter  of  about  0.5  mm.  had  taken 
place.  Growth  continued  for  a  short  time  only,  no  enlargement  being 
visible  after  June  30.  The  total  increase  in  diameter  for  the  season 
amounted  to  about  0.8  mm.,  and  activity  was  seen  to  extend  over  a  period 
of  140  days.  The  record  in  the  latter  part  of  the  season  was  characterized 
by  an  almost  entire  absence  of  the  daily  fluctuating  variation  in  diameter 


24 


DENDROGRAPHIC  MEASUREMENTS. 


of  the  trunk,  which  is  a  marked  feature  of  this  species.  This  may  be 
coupled  directly  with  the  reduction  of  the  transpiring  surface  to  a  fraction 
of  its  original  area. 

The  three  larger  and  lower  branches  were  alive  at  the  end  of  September 
1923.  These  were  vigorous  and  were  showing  some  upward  curvature  at 
the  tips  as  would  take  place  in  any  tree  from  which  the  top  of  the  main 
stem  had  been  removed.  The  soil-moisture  content  at  this  time  was  prob¬ 
ably  near  the  limit  of  availability,  being  very  low. 

Another  experiment  in  the  removal  of  part  of  the  trunk  and  foliage  of 
the  tree  was  made  with  Monterey  pine  No.  18,  which  was  in  moist  soil 
with  Nos.  16  and  18.  The  results  of  girdling,  and  of  removal  of  the  upper 
part  of  the  top  of  No.  16,  have  already  been  described. 

No.  18  was  about  17  years  old  and  the  bark  had  not  yet  begun  to  flake, 
being  green  under  the  dendrograph.  Like  Nos.  16  and  18,  more  than  one 
layer  of  wood  was  formed  every  year.  The  trunk  at  the  point  of  measure¬ 
ment  had  a  diameter  of  10  cm.  at  the  end  of  1923.  The  instrument  was  put 
in  place  October  23,  1922.  Enlargement  during  the  next  few  weeks  was 
indefinite  and  ceased  entirely  between  December  14  and  27.  Growth  was 
interrupted  between  January  25  and  February  15,  due  to  low  temperatures 
accompanying  a  storm.  A  total  increase  of  1.7  mm.  had  taken  place  by 
March  8,  at  which  time  the  trunk  was  cut  off  50  cm.  above  the  dendrograph 
and  2.2  meters  from  the  base.  Four  vigorous  branches  over  1  meter  long 
remained  above  the  instrument,  and  three  below,  in  addition  to  some  smaller 
and  more  slender  ones  which  soon  perished.  Enlargement  ceased  within  24 
hours  after  the  operation,  and  the  daily  variations  decreased  to  nearly  zero. 
The  record  was  now  a  direct  line,  nearly  horizontal,  with  some  slight  daily 
equalizing  variation  discernible  in  April,  which  became  marked  with  the 
advance  of  the  season.  No  further  enlargement  of  the  trunk  took  place 
during  the  season. 

The  chief  feature  of  interest  consisted  in  the  development  of  adventitious 
buds  at  various  places  on  the  trunk,  the  elongation  being  greatest  in  those 
which  were  on  the  terminal  part  of  the  stump.  The  results  in  this  tree  were 
not  essentially  different  from  those  obtained  from  No.  10.  Despite  the 
more  abundant  water-supply  and  the  greater  volume  of  leaves  remaining 
on  this  tree,  the  layer  of  wood  formed  in  the  first  year  after  topping  was 
less  than  in  No.  10.  The  trunk  was  cut  much  nearer  to  the  base  than  in 
No.  10,  however. 

EFFECTS  OF  DEFOLIATION. 

Topping,  or  the  removal  of  any  part  of  the  shoot  of  a  tree,  not  only 
lessens  the  transpiring  surface,  but  removes  accumulated  food  material  and 
excitatory  substances  which  might  be  in  transit  to  growing  regions  in  the 
trunk  below.  Defoliation,  if  properly  carried,  would  lessen  transpirational 
capacity  and  stop  the  formation  of  excitatory  substances  as  well  as  con¬ 
structive  material.  The  removal  of  leaves  from  trees  at  various  seasons  was 
carried  to  obtain  analytical  information  on  this  point.  A  small  tree,  No. 
19,  4  meters  in  height,  5.5  cm.  in  diameter  at  the  base,  and  about  10  years 
old,  standing  on  a  north-facing  slope,  was  selected  for  the  first  test.  A 
dendrograph  was  fitted  to  the  stem  near  the  base  on  October  23,  1922. 
Several  impulses  of  enlargement  occurred  in  October  and  November,  but 


EXPERIMENTAL  INVESTIGATIONS. 


25 


none  in  December.  Growth  for  the  season,  however,  began  on  January  3, 
1923,  being  interrupted  the  last  week  in  January  and  the  first  week  in 
February,  as  were  a  number  of  other  trees  already  described.  A  total 
increase  in  diameter  of  5.3  mm.  had  taken  place  by  March  8,  the  date  on 
which  defoliation  was  brought  about. 

All  of  the  leaves  formed  previous  to  this  season  were  plucked  out  by  being 
pulled  directly  in  their  axis,  in  such  manner  as  not  to  strip  the  stems  in  any 
degree,  the  scar  being  quickly  sealed  with  resin.  Some  of  the  leaves  were 
removed  on  the  afternoon  of  the  7th,  and  the  customary  contraction  did  not 
take  place  on  the  morning  of  the  next  day.  Defoliation  was  completed  in 
the  afternoon  and  no  further  enlargement  took  place  after  its  completion. 
The  record  was  now  a  direct  unbroken  line  with  only  very  slight  variations 
daily.  A  slight  enlargement  occurred  in  the  week  following  March  26,  but 
the  total  increase  was  very  small. 

Observations  on  the  condition  of  the  tree  on  May  18  showed  that  the 
terminals  of  the  main  stem  and  of  one  of  the  branches  had  undergone  some 
elongation,  but  as  no  measurements  had  been  made,  the  amount  could  not 
be  determined.  The  leaves,  which  had  attained  a  length  of  3  to  4  cm.  on 
the  terminals  of  the  branches,  stood  out  more  nearly  at  right  angles  to  the 
stems  than  in  normal  plants.  Measurements  on  June  4  showed  that  the 
maximum  length  of  the  newly  formed  stems  was  20  cm.,  with  most  of  them 
not  more  than  half  this  length.  The  maximum  length  of  the  young  leaves 
at  this  time  was  5  cm.,  and  the  “bottle  brush”  appearance  of  the  young 
shoots  was  very  striking. 

Equalizing  variations  had  been  abolished  by  defoliation,  but  were  again 
apparent  during  the  last  week  in  May,  and  were  clear  and  decisive  by 
June  14. 

About  this  time  some  slight  increase  began,  but  at  such  a  low  rate  that 
by  the  end  of  September  the  total  was  not  more  than  0.5  mm.  The  daily 
fluctuating  variations  showed  a  very  gentle  reversal  by  which  the  stem 
changed  but  little  in  volume  between  6  and  8  a.m.,  then  contracted  slowly 
until  about  4  p.m.,  when,  after  a  second  period  of  no  change,  a  swelling 
began. 

The  leaves  had  taken  on  a  position  more  nearly  normal  by  the  end  of 
September,  with  an  average  length  of  7  to  9  cm.  The  total  area  of  leaf- 
surface  at  this  time  was  probably  about  one-third  that  of  the  tree  in  its 
normal  condition  with  all  of  the  leaves  of  previous  seasons.  The  actual 
photosynthetic  capacity  of  the  foliage  had  probably  been  less  than  a  fourth 
of  the  normal.  Furthermore,  the  leaf-products  made  available  to  the  tree 
were  those  of  young  and  growing  leaves.  It  is  probable  that  these  did  not 
furnish  to  the  growing  regions  in  the  stems  construction  material  and 
excitatory  substances  of  the  same  kind  or  identical  proportions,  as  mature 
leaves  might  have  done. 

The  effect  of  defoliation  at  a  later  stage  of  the  season  was  tested  with 
Monterey  pine  No.  23,  which  was  about  12  years  old.  This  stood  near 
No.  19,  on  a  north-facing  slope,  and  was  about  7  meters  in  height  and 
6  cm.  thick  at  the  base  of  the  stem.  It  was  characterized  by  a  leader  of 
1922  over  a  meter  in  length,  and  had  made  an  extension  during  the  present 
season  of  60  cm.,  with  a  whorl  of  7  branches  40  to  50  cm.  in  length. 


26 


DENDROGRAPHIC  MEASUREMENTS. 


Some  of  the  secondary  branches  showed  no  growth  during  the  present 
season.  A  dendrograph  was  attached  on  May  28,  1923,  and  the  stem  was 
found  to  be  in  a  state  of  rapid  enlargement.  The  tree  had  probably  fol¬ 
lowed  a  course  similar  to  that  of  Nos.  17  and  19. 

Defoliation  was  carried  between  3  and  4  p.m.  on  June  4.  Leaves  of  a 
total  weight  of  2.27  kg.  were  removed,  and  as  the  average  weight  of  90 
leaves  was  1  gram,  it  was  estimated  that  the  total  number  removed  was 
about  244,000.  Here,  as  in  No.  19,  the  leaves  on  the  newly  formed  shoots 
were  left  untouched.  The  larger  branches  above  the  middle  of  the  stem 
had  made  elongations  of  as  much  as  40  mm.  and  the  young  leaves  borne 
on  them  were  as  long  as  10  cm. 

The  behavior  of  this  tree  was  in  vivid  contrast  with  that  of  No.  19,  which 
had  been  defoliated  3  months  earlier.  In  this  case,  enlargement  of  the 
trunk  and  the  daily  fluctuations  continued  in  a  manner  not  noticeably 
different  from  that  characterizing  the  action  of  the  tree  before  the  leaves 
were  removed.  The  weight  of  the  leaves  removed  was  estimated  to  be 
greater  than  from  No.  19,  and  the  young  leaves  remaining  had  nearly 
double  the  length  of  those  on  No.  19.  Furthermore,  the  removal  of  the 
leaves  was  not  accompanied  by  the  exudation  of  resin  to  an  amount  which 
was  seen  in  No.  19. 

The  defoliation  had  deprived  the  tree  of  a  large  part  of  its  transpiring 
surfaces,  and  it  was  now  proposed  to  replace  this  to  whatever  extent  might 
be  possible  by  connecting  an  exhaust  pump  to  the  main  stem  of  the  plant. 
A  staging  had  been  constructed  which  provided  a  small  platform  on  a  level 
with  the  median  part  of  the  terminal  shoot  internode  of  1922.  A  Nelson 
oil-vacuum  pump  had  been  mounted  on  this  platform  and  belted  to  an 
electric  motor  of  0.25  h.p.  A  line  of  pressure  tubing  of  5  mm.  caliber  was 
connected  with  a  short  section  with  large  diameter,  the  end  of  which  was 
fitted  with  an  encircling  clamp,  to  be  tightened  with  a  screw.  The  line  was 
interrupted  in  the  middle  by  T-tube  connecting  with  a  perpendicularly 
supported  mercurial  barometer  tube  open  at  the  upper  end.  A  slight  rain 
had  come  on  the  14th  and  had  begun  again  on  the  evening  of  the  15th, 
continuing  overnight,  so  that  on  the  forenoon  on  this  day  the  customary 
daily  contraction  of  the  stem  did  not  occur,  thus  furnishing  the  ideal  con¬ 
ditions  for  the  first  test  to  be  made.  The  apparatus  being  in  readiness,  the 
stem  was  cut  in  the  middle  of  the  internode,  where  the  diameter,  including 
the  bark,  was  25  mm.,  first  with  a  saw  directly  across,  then  the  cut  was 
made  oblique  by  slicing  away  the  wood  with  a  sharp  knife  until  about  twice 
the  circular  cut  surface  was  exposed.  A  layer  of  Canada  balsam  liquefied 
in  cedar  oil  was  applied  to  the  bark  immediately  below  the  cut,  the  open 
end  of  the  heavy  tube  was  worked  into  place  over  the  end  of  the  stem  until 
it  was  covered  for  a  length  sufficient  to  make  a  good  seal,  then  the  circular 
clamp  was  tightened.  The  pump  being  started  at  9h30m  a.m.,  the  mercury 
rose  in  the  pressure-gage  to  740  mm.  within  a  few  minutes.  The  customary 
contraction  of  the  stem  began  when  the  sky  cleared  after  llh30ra  a.m.,  and 
was  checked  when  over-clouding  came  on  at  2  p.m.  The  pump  was  now 
stopped  at  2h30m  p.m.  No  direct  effect  of  the  suction  on  the  end  of  the 
stem  could  be  detected.  The  pump  was  again  put  into  action  from  11  to 
2  p.m.  on  the  22d  and  again  maintained  a  column  of  mercury  of  745  mm., 


EXPERIMENTAL  INVESTIGATIONS. 


27 


appearing  to  accentuate  the  contraction  of  the  stem  as  denoted  by  the 
dendrographic  record. 

A  test  was  now  made  as  to  action  of  the  pump  on  the  stem.  The  con¬ 
nections  being  allowed  to  remain  intact,  the  stem  was  cut  off  below  the 
end  in  such  a  way  that  a  length  20  cm.  long  was  allowed  to  remain  con¬ 
nected  with  the  pump.  This  was  immediately  dipped  in  a  cylinder  of 
water  and  the  pump  started  at  3h10m  p.m.  After  a  half-hour,  29  c.  c.  of 
water  was  necessary  to  replace  the  amount  taken  up  in  this  manner  and 
appearing  in  the  exhaust  tubes.  It  is  to  be  seen,  therefore,  that  the  pump 
pulled  water  through  this  short  section  of  stem  at  a  rate  about  10  times 
that  which  would  result  from  the  action  of  the  top,  which  had  been  removed. 
It  is  not  probable  that  the  tree  under  any  circumstances  would  transpire 
water  through  the  foliage  on  the  separated  top  at  a  rate  more  than  double 
that  noted  above.  Thus,  the  top  might  remove  as  much  as  300  c.  c.  from 
stem  in  a  day,  while  the  pump  pulled  water  through  it  at  a  rate  which 
would  conduct  nearly  1,400  c.  c.  in  a  day. 

The  top  cut  from  the  tree  as  above  was  found  to  take  from  100  to  150 
c.  c.  of  water  daily  from  a  cylinder.  This  went  on  for  five  days,  when  the 
rate  fell  off  and  the  absorption  was  much  less. 

The  pump  connected  with  the  top  of  the  stem  of  the  tree  was  run  again 
from  9  a.m.  to  2h30m  p.m.  on  the  26th.  A  second  operation  of  equal  length 
was  made  on  the  27th.  No  effort  was  spared  in  the  attempt  to  detect  any 
possible  effect  of  the  suction  on  the  stem  on  growth.  It  first  appeared  that 
some  accentuation  of  growth  had  taken  place,  but  this  action  was  but  little 
different  from  that  shown  by  untreated  trees  of  corresponding  age  and 
development. 

The  pump  was  refitted  on  August  10.  At  first  the  vacuum  produced  by 
its  operation  was  equivalent  to  760  mm.  mercury,  but  this  soon  fell  to  720 
and  730  mm.  A  branch  near  the  base,  with  its  tip  cut  off  and  the  stump 
thrust  into  water,  took  in  60  c.  c.  of  water  on  the  first  day.  The  amount 
taken  decreased  day  by  day,  so  that  but  20  c.  c.  were  taken  in  on 
August  21.  The  pump  was  operated  for  3^2  hours  on  the  14th,  but  this 
did  not  increase  the  amount  taken  in  by  the  branch  with  its  tip  in  water. 
It  was  again  operated  on  the  21st  for  3  hours  without  discernible  results 
as  to  water  intake.  On  the  other  hand,  the  stem  showed  greater  increases 
on  the  two  or  three  days  following  the  operation  of  the  pump  than  before 
or  after  this  time.  Extended  experimentation  would  be  needed  to  make  an 
exact  estimate  of  the  effect  and  to  identify  the  physical  disturbances 
caused. 

Elongation  during  the  summer  was  noticeable  in  nearly  all  of  the 
branches,  being  greatest  in  the  larger  upper  ones,  in  which  the  new  axis 
was  5  or  6  cm.  long,  with  leaves  about  2  cm.  long.  The  most  striking 
feature,  however,  was  that  the  new  extensions  were  apogeotropic  and 
assumed  an  erect  position,  a  result,  presumably,  of  the  excision  of  the 
leader. 

It  was  noted  that  at  this  time  the  tips  of  all  of  the  branches  were  active 
and  that  all  of  them  had  turned  their  apices  upward,  some  of  them  having 
attained  a  directly  upright  position.  The  conjunction  of  all  of  the  buds  in 
this  action  would  not  ordinarily  be  attributed  to  the  effects  of  the  excision 


28 


DENDROGRAPHIC  MEASUREMENTS. 


of  the  leader.  It  seems  reasonable  to  suppose  that  either  the  defoliation 
or  the  action  of  the  pump  had  disturbed  the  flow  of  material.  The  lack  of 
some  substance  ordinarily  derived  from  the  old  leaves,  or  from  the  leader,  or 
the  removal  of  some  material  by  the  pump,  may  have  altered  the  character 
of  the  geotropic  equilibrium  of  the  branches. 

A  cessation  in  the  enlargement  of  the  trunk  came  at  the  first  of  September, 
but  was  noticeable  again  on  the  11th;  exactly  equal  diameters  were  regis¬ 
tered  on  the  11th  to  16th,  then  a  slow  increase  was  visible  which  continued 
to  include  the  26th;  now  came  another  period  of  clear  days  and  high  tem¬ 
peratures  in  which  the  daily  variations  were  equalized,  the  total  increase 
in  diameter  since  defoliation  amounting  at  that  time  to  3  mm.  In  any 
comparison  that  might  be  made  with  the  activity  of  No.  19,  which  was 
defoliated  in  March,  before  the  young  leaves  had  attained  half  size  and 
before  more  than  a  small  part  of  the  leaf-products  of  the  old  leaves  were 
available,  it  is  to  be  seen  that  in  No.  23  the  old  leaves  were  active  for  3 
months  longer  and  the  young  leaves  had  reached  a  much  more  advanced 
stage  before  defoliation.  The  supply  of  constructive  material  and  of 
excitatory  agents,  as  well  as  of  material  from  the  soil,  would  be  more  nearly 
normal  because  of  this  extended  activity  of  the  leaves. 

The  pump,  which  had  been  kept  attached  to  the  upper  end  of  the  trunk, 
was  again  operated  for  5  hours  on  October  1,  the  sky  being  overcast,  which 
tended  to  cause  some  enlargement  of  the  trunk.  The  increase  which  took 
place  in  24  hours,  however,  was  much  greater  than  might  be  attributed  to 
such  a  condition,  the  pen  rising  3  mm.  higher  on  the  record-sheet  than  on 
the  previous  day,  indicative  of  an  actual  swelling  of  nearly  0.2  mm.  in  24 
hours.  Such  an  effect  of  the  vacuum  on  the  upper  end  of  the  stem  is  in 
agreement  with  results  previously  obtained  and  described  above. 

The  third  tree  in  this  series,  Monterey  pine  No.  25,  wras  a  smaller  one, 
with  a  trunk  5  cm.  in  diameter  and  with  a  height  of  about  4  meters.  This 
tree  was  about  12  years  old  and  retained  nearly  all  of  its  branches,  which 
were  still  leafy  to  their  bases.  The  dendrograph  attached  to  the  basal 
portion  on  September  25, 1923,  showed  that  the  enlargement  of  the  stem  had 
come  down  to  a  very  low  rate,  probably  by  reason  of  the  low  soil-moisture 
content.  The  leaves,  including  those  formed  in  the  beginning  of  the  year, 
were  removed  on  the  afternoon  of  October  1,  being  pulled  directly  out  to 
avoid  laceration  of  the  bark.  The  day  was  overcast.  The  operation  left 
the  tree  devoid  of  green  surfaces  or  of  any  avenues  for  transpiration  outside 
of  the  buds,  lenticels,  and  rifts  in  the  bark,  the  leaf-scars  being  quickly 
sealed  by  resinous  excretion.  The  total  weight  of  the  leaves  removed  was 
4.2  kg. 

The  average  weight  of  leaves  was  that  of  54  to  the  gram,  as  compared  to 
90  to  the  gram  in  No.  23  in  June,  only  the  leaves  of  the  previous  years  being 
included  in  the  estimate  of  No.  19,  while  all  were  taken  in  No.  25.  The 
number  taken  from  No.  23  was  244,000  while  the  total  stripped  from  No. 
25  was  estimated  at  227,000.  It  is  obvious  that  the  actual  leaf-surface  of 
the  two  trees  was  about  equivalent.  Nos.  19  and  23  had  at  all  times 
one-fifth  of  their  leaf-surfaces  in  a  functioning  condition,  while  the  only 
chlorophyll  in  No.  25  after  the  stripping  was  that  carried  in  the  young  bark. 


EXPERIMENTAL  INVESTIGATIONS. 


29 


The  daily  variation,  which  had  risen  to  a  constant  maximum  for  the 
preceding  5  days,  had  an  amplitude  of  0.3  mm.,  or  1  part  in  170.  This  was 
reduced  to  a  minimum  on  the  day  following  defoliation.  The  stem  had 
undergone  a  slow  swelling  during  the  night  and  only  a  minute  contraction 
was  to  be  seen  at  midday.  The  record  now  became  a  direct  line,  with  barely 
discernible  contractions  in  the  mid-day  period.  The  further  behavior  of 
this  tree  and  of  Nos.  19  and  23  will  be  discussed  in  a  future  paper. 

PATH  AND  RATE  OF  MOVEMENT  OF  LIQUIDS  IN  STEMS  OF 

MONTEREY  PINE. 

For  the  purposes  of  the  present  studies,  the  use  of  solutions  of  dyes 
seemed  to  furnish  the  best  means  of  following  the  path  of  liquids  through 
stems  and  along  layers  of  wood.  Reliance  was  placed  chiefly  in  the  use  of 
Fuchsin  S  (Griibler  &  Co.).  This  basic  dye  was  found  by  Ruhland1  to 
have  a  high  speed  of  absorption  or  penetration  into  cells.  Its  colloidal  con¬ 
dition  makes  its  movements  through  the  layers  of  the  cell  depend  upon  its 
capillary  activity  rather  than  on  ionic  velocity. 

The  use  of  the  dye  here  was  one  in  which  its  diffusion  through  cell-walls 
and  along  intercellular  spaces  was  concerned,  and  no  effort  was  made  to 
measure  its  penetration  of  the  living  cells  of  the  medulla  or  its  rays,  or  the 
cortex  and  cambium. 

The  first  test  was  made  in  July  1923  with  the  shoot  of  a  small  tree  which 
near  its  base  had  a  diameter  of  1  cm.  and  5  cylindrical  layers  of  wood, 
indicating  a  low  annual  rate  of  growth.  This  tree  was  cut  off  a  meter  from 
the  tip  and  the  shoot  immediately  stepped  into  a  vessel  containing  a 
Fuchsin  solution,  1  part  of  the  dye  to  1,000  of  water.  The  color  was  found 
at  the  extreme  tip  of  the  stem  48  hours  later,  100  c.  c.  of  the  solution  having 
been  taken  up.  The  basal  part  of  the  tree,  which  was  also  about  a  meter 
in  length,  was  bent  over  and  the  cut  surface  immersed  in  a  dye  solution. 
Staining  was  visible  downward  for  a  distance  of  90  cm.,  there  being  no 
branches  on  this  part  of  the  stem.  The  above,  however,  does  not  represent 
the  maximum  rate  at  this  season  in  such  small  shoots,  which  is  always 
greater  moving  upwardly  than  the  reverse,  as  another  shoot  125  cm.  long 
conducted  the  dye  solution  to  its  tip  in  48  hours. 

Another  small  tree,  14  mm.  in  diameter  at  the  base  and  showing  5  layers, 
was  cut  off  and  the  base  set  in  some  of  the  same  solution,  the  leaf-system 
being  left  entire  and  active.  In  20  hours  the  color  was  discernible  at  125 
cm.  from  the  base  and  70  c.  c.  of  the  liquid  had  been  absorbed.  The  severed 
basal  part  of  another  small  tree  of  somewhat  larger  diameter  was  inverted 
with  the  stump  of  the  terminal  portion  in  a  bottle  of  the  dye.  The  portion 
of  the  tree  used  bore  several  vigorous  branches.  The  dye  had  run  to  a 
length  of  80  cm.  from  the  tip,  and  at  this  distance  had  passed  the  bases  of 
most  of  the  branches  which  would  exert  a  pull  by  transpiration  on  the 
movements  of  the  liquid,  and  some  color  had  gone  into  them. 

A  tree  about  3  meters  in  height  and  22  mm.  in  diameter  at  the  base  was 
cut  off  and  the  base  of  the  excised  shoot  stepped  in  a  vessel  of  dye  at  4  p.m. 

1  W.  Ruhland.  Studien  ueber  die  Aufnahme  von  Kolloiden,  durch  die  pflanzliche  Plasma- 
haut.  Jahrb.  f.  Wiss.  Botan.,  51,  376-431.  1912. 


30 


DENDROGRAPHIC  MEASUREMENTS. 


The  stain  was  found  at  a  height  of  180  cm.  44  hours  later.  At  this  height 
the  color  had  been  diverted  into  the  several  members  of  a  whorl  of  branches. 
The  tip  of  a  similar  small  tree  being  cut  off,  the  stump  was  immersed  in  a 
dye  solution  and  in  the  same  time  the  color  had  gone  down  the  stem  53  cm., 
where  it  was  diverted  into  a  whorl  of  branches  formed  during  the  previous 
year. 

A  small  tree  growing  on  a  nortlrward-facing  slope,  which  was  in  a  thick 
stand,  so  that  it  was  but  7  cm.  at  the  base  and  8  meters  in  height,  was  cut 
off  near  the  base  on  Saturday,  July  14,  the  base  of  the  trunk  being  stepped 
into  a  vessel  containing  the  Fuchsin  solution,  wThile  the  trunk  was  kept  in  a 
position  nearly  erect,  leaning  on  a  larger  tree.  The  annual  layers  at  the 
base  were  21  in  number,  showing  that  the  tree  must  have  been  about  22 
years  old. 

The  absorption  of  the  dye  solution  was  so  rapid  at  first  that  700  c.  c.  was 
absorbed  in  48  hours;  the  next  24  hours  about  400  c.  c.  At  the  end  of  this 
3-day  period  the  presence  of  the  dye  was  discernible  3.5  meters  from  the 
base,  the  end  of  the  colored  zone  being  distinguished  by  the  fact  that  the 
color  could  be  seen  only  in  the  three  outermost  layers  and  also  appeared 
in  a  thicker  layer  much  nearer  the  center  and  separated  from  the  other 
colored  layers.  Near  the  base  the  heart  of  about  8  layers  remained  totally 
uncolored. 

A  small  tree  about  3  meters  in  height  was  topped  in  July  by  cutting  away 
the  terminal  half  of  the  leader  or  extension  of  the  shoot  formed  during  the 
current  season.  It  was  left  untouched  at  the  base  and  the  stump  was 
thrust  into  a  solution  of  the  dye.  Two  weeks  later  the  color  had  come  down 
through  the  stem  only  so  far  as  the  first  node  or  whorl  of  branches,  passing 
through  all  of  the  wood  which  was  of  this  season’s  formation  without 
noticeable  differentiation.  But  little  of  the  color  had  gone  out  into  the 
branches.  In  this  case  the  stem  was  in  full  connection  with  the  root  system 
and  the  dye  had  passed  down  the  stem  to  a  point  where  it  would  have  met 
a  flow  coming  upward  and  going  out  into  the  branches  and  leaves.  It  is 
evident  that  in  all  of  these  cases  the  movement  is  the  resultant  of  three 
factors:  the  capillarity  of  the  dye,  the  upward  stream  from  the  roots,  and 
the  pull  of  transpiration  from  the  leaves. 

The  downward  movement  of  the  dye  was  in  no  case  equivalent  to  the 
rate  upward,  but  in  every  instance  the  color  was  deflected  laterally  into 
branches.  Furthermore,  the  cross-section  of  the  stem  increases  downward, 
which  would  tend  to  lessen  the  rate  of  longitudinal  movement. 

It  is  obvious  that  with  the  constant  absorption  of  the  dye  the  maximum 
rates  would  be  obtained  by  observations  for  short  periods  and  for  short 
sections  of  stems.  The  movement  in  the  young  tree  3  meters  in  height 
must  have  been  very  rapid  at  first,  although  at  the  end  of  44  hours  the 
total  was  180  cm.,  or  about  4.4  cm.  per  hour.  The  largest  tree  tested  in  this 
manner  was  7  cm.  in  diameter  at  the  base  and  the  rate  calculated  for  4  days 
was  about  4  cm.  per  hour.  The  maximum  was  6  cm.  per  hour  in  a  length 
of  125  cm.  The  maximum  downward  was  4  cm.  per  hour.  These  rates 
are  much  less  than  those  observed  late  in  the  season. 

The  path  of  solutions  furnished  the  stem  in  this  manner  is  seen  to  lie 
chiefly  in  the  wood  formed  during  the  previous  two  or  three  seasons.  When 


EXPERIMENTAL  INVESTIGATIONS. 


31 


the  base  of  a  tree  cut  from  its  base  is  stepped  into  a  vessel  containing  the 
dye,  however,  distinct  upward  movements  may  take  place  in  some  layers 
toward  the  center  in  a  very  unequal  manner. 

These  tests  were  repeated  in  October,  when  nearly  all  of  the  trees  had 
reached  a  quiescent  stage  as  to  growth,  and  attention  was  paid  to  the  pos¬ 
sible  effects  of  the  suctions  exerted  by  a  vacuum  connected  with  the 
terminal  part  of  the  stem. 

The  principal  experiments  were  carried  out  with  four  small  trees.  The 
stems  were  set  in  the  solution  of  Fuchsin,  as  noted  above,  on  October  8. 
One,  which  was  4  cm.  in  diameter  at  the  base,  about  12  years  old  and  bear¬ 
ing  small  branches,  was  connected  with  the  Nelson  vacuum-pump.  The 
top  was  cut  off  below  the  uppermost  whorl  of  branches,  leaving  an  exposed 
end  about  2  cm.  across.  The  end  of  a  small  section  of  pressure  hose  was 
clamped  about  this,  and  when  the  pump  was  started  at  10h15m  a.m.  the 
mercury  quickly  rose  to  730  mm.  in  the  gage.  A  second  tree,  4.5  cm.  in 
diameter  at  the  base,  about  5  meters  in  height,  and  bearing  branches  about 
equivalent  to  the  one  connected  with  the  pump,  was  topped  in  the  same 
way  with  the  cut  upper  end  left  exposed.  A  third  smaller  tree,  5  meters 
in  height,  with  numerous  branches,  only  4  cm.  in  thickness  at  the  base  and 
about  14  years  old,  was  set  in  the  dye.  This  tree  bore  many  small  branches 
and  would  have  a  relative  transpiring  capacity  much  above  the  first  two 
trees  which  had  been  topped.  A  fourth  tree,  still  smaller,  being  only  2.2  cm. 
in  diameter  at  the  base,  4  meters  in  height,  about  12  years  old,  and  with  few 
branches  and  hence  relatively  small  transpiring  capacity,  was  included  in 
the  group.  The  day  was  warm,  still,  and  sunny,  with  only  an  occasional 
cloud. 

The  pressure  in  the  pump  system  fell  to  620  mm.  of  mercury  an  hour 
after  the  beginning,  and  to  520  at  the  end  of  the  5-hour  test,  due  to  a 
defective  joint. 

The  test  was  ended  5  hours  later  and  all  of  the  stems  examined  for  the 
presence  of  the  dye.  The  rates  shown  by  all  were  in  excess  of  those  noted 
above,  which  were  measured  during  the  season  of  rapid  growth  in  June. 
The  dye  was  discernible  in  a  very  faint  stain  in  the  control,  which  had 
been  topped  like  the  one  under  the  pump  at  57  cm.  from  the  base,  ending 
at  a  node  but  by  no  means  being  in  such  quantity  as  to  be  traced  out  into 
a  branch. 

The  tree  to  which  the  pump  was  attached  showed  the  dye  as  strongly 
staining  outer  rings  to  a  distance  of  65  cm.  from  the  base,  as  it  happened, 
near  a  node  but  not  going  out  into  branches. 

The  smaller  tree  with  many  branches  showed  the  stain  to  a  distance  of 
55  cm.  from  the  base,  terminating  at  a  node.  The  smallest  tree,  which  had 
a  diameter  of  only  2  cm.  at  the  base,  showed  the  highest  rate  yet  measured 
in  any  of  these  trees,  the  stain  having  traversed  the  stem  to  a  distance  of 
80  cm.  The  rates  of  conduction  of  the  dye  in  sufficient  quantity  to  be 
observable  were,  therefore,  11,  13,  11,  and  16  cm.  per  hour.  It  was  notable 
that  while  the  stem  subjected  to  the  action  of  the  pump  did  not  greatly 
exceed  the  rate  of  its  control,  yet  the  amount  of  dye  shown  was  many  times 
greater.  The  stain  in  this  tree  was  marked  in  the  second  and  fourth  layers 
of  wood,  in  the  control  in  the  third  and  fourth,  as  also  in  the  one  with  many 


32 


DENDROGRAPHIC  MEASUREMENTS. 


branches.  The  smallest  tree  with  the  highest  rate  had  the  second  ring  which 
was  formed  in  1922  most  heavily  stained.  It  is  possible  that  two  layers  of 
wood  had  been  formed  in  1923.  The  formation  of  two  or  more  layers  in 
a  year  by  these  young  trees  may  be  held  to  account  for  the  apparent 
departure  from  the  conclusion  that  conduction  is  greatest  in  the  wood  of  the 
previous  two  years.  It  would  seem  that  when  two  layers  are  formed  in 
the  same  year  they  are  not  equal  in  their  conducting  capacity.  The  trees 
having  been  shortened  by  the  lengths  indicated  above,  they  were  set  in  the 
dye  immediately  to  test  the  rate  of  conduction  from  4  p.m.  until  the  next 
morning,  the  pump  not  being  operated.  All  of  the  trees  had  in  the  aggre¬ 
gate  taken  up  1,550  c.  c.  of  liquid  in  5  hours. 

At  8  a.m.  on  the  following  morning,  after  16  hours,  the  four  trees  had 
taken  up  1,450  c.  c.  of  dye.  The  one  attached  to  the  pump,  which  had  not 
been  operated  during  this  time,  had  taken  the  dye  up  60  cm.,  its  control 
60  cm.,  one  node  being  passed  in  each  tree,  and  the  dye  being  seen  farthest 
up  the  stem  in  the  fourth  layer  in  the  one  attached  to  the  pump  and  in  the 
fourth  and  fifth  layers  in  the  control.  The  stain  had  gone  up  80  cm.  in  the 
one  with  many  leafy  branches,  the  conduction  being  most  pronounced  in 
the  first  and  fourth  layers,  after  passing  2  nodes.  The  smallest  tree  had 
taken  the  dye  upward  to  a  distance  of  70  cm.,  past  one  node  in  the  second 
and  fourth  layers.  It  was  to  be  seen  that  the  rate  in  the  one  attached  to 
the  pump  was  identical  with  the  control  during  16  hours  when  the  pump 
was  not  in  operation.  The  rate  in  the  two  largest  was  less  than  one-third 
that  in  the  daytime,  and  also  in  the  smallest.  The  rate  in  the  one  with 
many  leafy  branches  was  highest.  The  rates  arranged  in  the  same  order 
as  given  previously  were  about  4,  4,  5,  and  4.4  cm.  per  hour.  The  lessened 
rate  may  be  connected  directly  with  decrease  in  transpiration  due  to  the 
narrowed  stomatal  slits  of  the  leaves  and  the  lowered  temperature. 

The  pump  being  started  at  8  a.m.  on  the  following  morning,  a  vacuum 
of  500  to  600  mm.  of  mercury  was  set  up,  and  the  tree  attached  showed 
stain  at  a  distance  of  65  cm.  in  the  second  layer  after  7  hours.  The  distance 
traversed  in  the  control  during  the  same  time  was  50  cm.,  the  stain  being 
in  the  second  layer  at  the  extremity.  The  leafy  tree  showed  stain  at  a 
distance  of  50  cm.  at  the  first  node,  which  bore  a  number  of  branches.  The 
stain  was  in  the  second  layer.  The  smaller  tree  was  stained  to  a  distance 
of  65  cm.  in  the  second  layer.  The  rates  for  this  daylight  period,  given  in 
the  same  order  as  before,  were  9,  7,  7,  and  9  cm.  per  hour.  The  dye  was 
seen  to  travel  farther  than  in  the  control,  although  it  did  so  at  night,  when 
the  pump  was  not  operating.  All  of  these  rates  were  less  than  the  day 
before.  It  is  to  be  noted  that  the  suction  exerted  by  the  pump  was  less  than 
on  the  previous  day.  The  highest  rate  continued  to  be  shown  by  the  small 
tree  in  which  the  woody  layers  were  thinnest. 

The  conduction  of  the  dye  was  taken  again  on  October  10  at  8  a.m.,  after 
16  hours  with  the  pump  not  operating.  The  tree  to  which  the  pump  was 
attached  showed  a  rate  of  3  cm.  per  hour,  which  was  near  that  of  the  control 
which  was  slightly  higher.  The  greatest  distance  was  reached  in  the  fourth 
layer  in  both.  The  rate  in  the  one  with  many  branches  was  slightly  less 
than  3  cm.  per  hour  in  the  second  and  fourth  layers  and  it  had  not  reached 
a  node.  The  dye  had  penetrated  clear  of  the  last  node  into  the  leader  at 


EXPERIMENTAL  INVESTIGATIONS. 


33 


the  rate  of  3.5  cm.  per  hour,  staining  the  layer  formed  in  1922  in  the 
internode  below.  The  material  was  now  set  up  for  a  daylight  test.  The 
smallest  tree  was  discarded.  The  pump  connection  was  shifted  to  the  apex 
of  the  one  hitherto  used  as  a  control,  which  had  a  length  of  2.2  meters 
remaining.  The  vacuum  showed  above  740  mm.  of  mercury  on  the  gage 
at  the  beginning  of  the  experiment.  Five  hours  later  the  dye  had  been 
taken  up  to  a  distance  of  only  25  cm.  in  the  trunk  connected  with  the  pump, 
65  cm.  in  the  one  which  had  been  previously  under  the  pump,  and  35  cm. 
in  the  one  with  many  branches. 

In  the  succeeding  16  hours,  including  the  night,  the  stem  with  many 
branches  had  conducted  the  dye  upward  to  the  last  whorl  of  leaves,  a  dis¬ 
tance  of  25  cm.,  which  was  at  the  rate  of  1.5  cm.  per  hour,  the  one  attached 
to  the  pump  on  the  previous  day  20  cm.,  and  the  one  originally  used  as  a 
control  25  cm.,  all  of  which  were  seen  to  be  much  less  than  in  any  daytime 
period.  After  every  test  the  stems  were  shortened,  of  course.  All  were  now 
discarded  except  a  short  section  of  the  one  originally  attached  to  the  pump, 
of  which  a  length  of  but  50  cm.  remained,  and  had  two  small  branches,  and 
the  one  originally  its  control,  which  was  much  longer  for  obvious  reasons, 
having  a  length  of  1.5  meters.  The  pump  attached  to  this  longer  stem 
was  started  before  9  a.m.  on  October  11,  the  day  being  warm,  still,  and 
sunny.  At  the  end  of  5  hours  the  dye  had  been  drawn  in  quantity  through 
the  stem,  1.25  meters  in  length,  while  it  had  gone  only  10  cm.  in  the  other 
or  shorter  one.  The  effect  of  the  vacuum  on  the  end  of  a  stem  in  acceler¬ 
ating  the  conduction  of  liquids  is  direct  and  marked. 

The  test  was  repeated  with  larger  trees,  both  of  which  had  grown  near 
the  north  side  of  the  laboratory  and  hence  were  slender  and  somewhat 
attenuated.  One  to  which  the  pump  was  attached  was  5.5  cm.  in  diameter 
at  the  base,  8  meters  in  height,  and  about  14  years  old.  The  leader  and 
some  of  the  internode  of  1922  were  cut  away  to  secure  suitable  thickness 
for  the  pump  connection,  the  stem  remaining  having  a  length  of  6.5  meters, 
the  base  being  set  in  a  solution  of  Fuchsin  1  part  to  1,000  of  water.  As  a 
control,  a  second  tree  about  12  or  13  years  old,  5  cm.  in  diameter  at  the 
base,  and  7  meters  high,  was  cut  and  its  base  set  in  the  same  vessel  of  dye. 
This  tree  was  not  topped.  The  terminal  which  was  removed  from  the  other 
tree  bore  leaves  which  were  estimated  to  weigh  800  grams,  and  as  these 
would  run  45  to  54  to  the  gram,  it  is  to  be  seen  that  40,000  leaves  were 
removed,  which  were  taken  to  constitute  about  one- fourth  of  the  foliage 
of  the  tree. 

The  pump  was,  therefore,  in  the  position  of  replacing  one-fourth  the 
foliage  of  the  tree,  and  if  an  acceleration  of  conduction  was  found  it  would 
tend  to  show  that  the  pump  gave  a  ‘Transpiration  pull”  equivalent  to  and 
in  excess  of  that  of  the  foliage  and  stems  removed. 

The  control  tree  had  taken  the  dye  up  to  a  distance  of  75  cm.  from  the 
base  in  the  third  and  fourth  layers  at  the  end  of  5  hours.  The  tree  con¬ 
nected  with  the  pump  had  taken  the  dye  up  to  only  50  cm.  It  was  noted 
that  this  trunk  was  more  highly  resinous  than  the  other  one. 

The  control  stem  conducted  the  dye  130  cm.  in  the  18  hours  between 
3  p.m.  and  9  a.m.,  the  color  being  farthest  extended  in  the  outermost  layer 
on  one  side  and  in  the  third  and  fourth  layers  on  the  other.  The  rate  during 


34 


DENDROGRAPHIC  MEASUREMENTS. 


this  period,  including  the  evening,  night,  and  morning,  was  7  cm.  per  hour 
as  compared  with  15  cm.  per  hour  during  the  initial  daylight  period  of  5 
hours.  The  dye  diffused  to  an  extent  of  65  cm.  in  the  one  attached  to  the 
pump,  but  which  was  not  operated  during  this  18-hour  period.  The  rate 
was  thus  seen  to  be  3.6  cm.  per  hour,  and  the  color  was  principally  in  the 
second  layer.  The  tree  to  which  the  pump  was  attached  may  therefore 
seem  to  have  a  lower  rate  than  the  control.  That  the  vacuum  at  the  tip 
had  exerted  some  effect  may  be  inferred  from  the  fact  that  the  daylight 
rate  of  the  control  was  about  twice  that  of  the  night  rate,  while  the  day¬ 
light  rate  of  the  one  with  the  pump  attached  was  nearly  three  times  the 
night  rate  with  the  pump  not  in  operation.  After  the  above  measurements 
had  been  made,  the  pump  was  set  in  operation  at  9  a.m.  on  October  13.  The 
length  of  this  stem  was  now  about  4  meters,  and  the  cutting  away  of  the 
basal  part  in  making  the  determinations  as  above  had  taken  but  few  of  the 
branches,  so  that  its  transpiration  capacity  would  be  but  slightly  lessened. 
The  greater  lengths  cut  from  the  control  left  a  length  of  but  2.5  meters  from 
the  base  to  the  tip  of  the  leader,  although  the  total  number  of  leaves  on  this 
section  was  estimated  to  be  but  little  below  that  of  the  stem  attached  to 
the  pump. 

After  5  hours  of  daylight  the  dye  had  stained  the  control  to  a  length  of 
45  cm.,  showing  a  rate  of  9  cm.  per  hour.  The  color  had  gone  up  the  stem 
to  which  the  pump  was  attached  a  distance  of  25  cm.,  showing  a  rate  of  5 
cm.  per  hour.  The  acceleration  in  the  control  by  daylight  conditions  was 
nearly  30  per  cent;  the  acceleration  of  the  stream  in  the  one  to  which  the 
pump  was  attached  and  operating  under  daylight  conditions  was  over  40 
per  cent.  The  remaining  lengths  were  placed  with  their  bases  in  the  dye  at 
2h30m  p.m.  Twenty-four  hours  later  the  dye  had  passed  up  the  control 
90  cm.  in  the  outermost  layer  of  wood  and  80  cm.  in  the  one  to  which  the 
pump  had  been  attached  but  not  operated.  The  first  and  third  layers  were 
stained  in  the  last  named  specimen. 

It  is  apparent  that  the  rate  of  flow  of  solutions  of  stain  may  be  much 
greater  in  the  Monterey  pine  late  in  the  season  than  in  the  stage  of  rapid 
growth.  Furthermore,  the  well-known  fact  that  the  sap  travels  most  in 
the  wood  of  the  two  previous  years  is  confirmed.  In  the  trees  which  form 
two  or  more  layers  yearly  the  greatest  conduction  in  the  autumn  is  in  the 
wood  that  was  formed  early  in  that  year  and  early  in  the  previous  year, 
the  intervening  and  interior  layers  being  free  from  the  stain.  If,  as  the 
staining  suggests,  there  is  but  little  stain  in  this  intermediate  layer,  a  pos¬ 
sibility  is  opened  for  the  consideration  of  the  clear  layer  as  a  possible  path 
for  a  downwardly  moving  stream.  That  material  might  move  both  upward 
and  downward  in  the  wood  was  proposed  by  Jones,  Edson,  and  Morse1  in 
1903  in  connection  with  the  study  of  sap-flow  in  the  sugar  maple.  This 
view  of  the  possibilities  has  also  been  taken  up  approvingly  by  Professor 
H.  H.  Dixon.2  Some  experiments  dealing  with  this  matter  are  to  be  carried 
out  in  this  laboratory. 

1  Jones,  Edson,  and  Morse.  The  maple-sap  flow.  Bull.  Vermont  Agric.  Exper.  Station. 
1903. 

2  H.  H.  Dixon.  Nature,  111,  236  and  547.  1922. 

J.  Adams.  The  translocation  of  carbohydrates  in  sugar  maple.  Nature,  112,  207..  1923. 


EXPERIMENTAL  INVESTIGATIONS. 


35 


Still  another  association  of  facts  is  that  the  woody  trunk  of  the  tree 
assumes  the  greatest  diameter  in  the  course  of  the  daily  variations  at  the 
time  the  upward  stream  is  moving  at  its  lowest  rate,  which  is  simply  another 
form  of  stating  that  the  loss  from  the  leaves  is  at  a  minimum  and  the 
amount  of  liquid  to  be  moved  to  the  top  of  the  trunk  is  least  at  this  time. 

The  actual  rate  of  movement  of  upwardly  bound  solutions  in  the  stems 
of  this  pine  make  it  an  especially  favorable  object  for  experimental  modi¬ 
fications.  The  foregoing  results  are  conclusive  evidence  that  the  main¬ 
tenance  of  a  vacuum  which  will  hold  up  a  column  of  mercury  740  mm.  in 
height  in  replacement  of  one-fourth  of  the  leaves  of  a  shoot  will  result  in 
acceleration  through  a  stem  up  to  6.5  meters  and  probably  to  greater 
lengths. 

REVERSIBLE  VARIATIONS  IN  VOLUME  INDEPENDENT  OF 

GROWTH. 

That  growing  cell-masses,  and  that  plant-members  variously  made  up  of 
living  cells  and  woody  structures,  may  undergo  daily  variations  in  volume 
has  been  found  by  all  observers  who  have  dealt  adequately  and  accurately 
with  measurement  of  growth.  The  shoots  of  mesophytic  plants  of  the 
types  ordinarily  used  for  study  have  a  higher  rate  of  transpiration  in  the 
daytime  than  at  night.  The  stems  and  other  organs  of  such  plants  may 
show  a  lessened  rate  of  growth  during  the  daytime,  or  in  the  case  of  mature 
tissues  may  actually  contract.  The  observation  of  such  facts  was  in  all 
probability  the  basis  for  the  mistaken  conclusion  that  light  retards  growth, 
a  notion  which  is  still  held  by  many  physiologists  with  respect  to  the  higher 
plants.  As  will  be  shown  in  subsequent  sections  of  this  paper,  some  plants, 
like  the  cacti,  show  the  greatest  enlargement  in  the  daytime  after  a  manner 
nearly  the  reverse  of  that  of  woody  trees,  fruits,  and  tubers.  The  contrac¬ 
tion  of  a  cell-mass  may  be  due  to  the  direct  loss  of  water  from  its  surface, 
or,  as  in  other  cases,  including  the  tomato,  the  walnut,  and  the  squash,  the 
supply  of  water  comes  to  these  structures  through  the  stems  acting  as  a 
common  conduit  from  which  the  leaves  also  draw  water.  A  state  of  com¬ 
petition  is  set  up  and  the  leaves  may  show  the  greatest  transpiration 
coincidentally  with  the  fruit  or  nut,  so  that  its  shrinkage  becomes  accen¬ 
tuated  by  reason  of  an  inadequate  water-supply. 

A  third  condition  is  represented  by  the  tuber  of  Solarium.  These  struc¬ 
tures  are  thickened  lateral  underground  branches,  are  at  the  ends  of  stem 
conduits,  and  water  must  flow  into  them  chiefly  by  imbibition  of  the  newly 
and  continuously  formed  carbohydrates  from  the  main  stems.  The  tran¬ 
spiration  from  the  surfaces  must  be  so  low  as  to  be  negligible  when  the 
tubers  are  normally  covered  with  moist  soil.  It  has  been  shown,  however, 
that  when  exposed  to  the  air  the  direct  water-loss  may  be  so  great  as  to 
give  rise  to  variations  of  the  same  kind  as  those  shown  by  the  tomato.  In 
all  of  these  cases  the  shrinkage  is  greatest  when  the  stomatal  slits  of  the 
leaves  are  widest.  The  action  of  these  organs  has  been  found  to  be  deter¬ 
minative,  so  that  in  some  plants,  such  as  the  cacti,  transpiration  is  greatest 
and  shrinkage  is  most  marked  in  the  evening  and  at  night,  instead  of  during 
the  period  when  evaporation  from  a  free  water-surface  would  be  greatest. 
In  other  instances,  such  as  the  leaves  of  Mesembryanthemum,  the  effect  of 


36 


DENDROGRAPHIC  MEASUREMENTS. 


high  temperatures  and  open  stomata  is  to  produce  the  greatest  water-loss 
and  resultant  shrinkage  at  midday,  at  which  time,  however,  the  slits  of  the 
stomata  begin  to  close  and  the  shrinkage  is  lessened. 

The  trunk  of  the  tree  cactus  ( Carnegiea  gigantea )  consists  of  a  central 
woody  cylinder  inclosing  a  large  medulla,  the  diameter  of  which  is  not  more 
than  half  that  of  the  entire  trunk.  External  to  it  is  a  very  thick  cortex, 
capable  of  hydration  and  dehydration  to  a  marked  degree,  and  having  a 
capacity  for  growth  which  is  not  well  defined  or  known.  These  conditions 
are  to  be  taken  into  account  in  the  consideration  of  the  fact  that  this 
singular  tree  shows  a  behavior  in  equalizing  variations  almost  opposite 
those  of  all  other  trees  which  show  the  greatest  diameter  at  sunrise  and 
the  least  in  mid-afternoon. 

The  daily  variations  of  the  trunk  of  a  woody  tree  illustrate  the  hydration 
and  dehydration  of  living  cells  as  in  the  foregoing  types,  and  in  addition 
display  an  action  of  the  woody  cylinder  of  the  trunk  which  would  have  an 
inevitable  intimate  connection  with  the  problems  encountered  in  the  study 
of  the  ascent  of  sap.  As  has  been  shown  in  the  discussion  of  the  daily  vari¬ 
ations  in  trunks,  there  is  a  shrinkage  in  trees  in  an  inactive  condition  at 
sunrise,  and  it  continues  until  mid-afternoon  or  evening,  when  recovery 
begins  and  the  cylinder  slowly  returns  to  its  maximum  dimensions,  which 
are  reached  at  daybreak.  Such  an  action  in  the  Monterey  pine  is  directly 
coincident  with  the  general  action  of  the  stomata.  According  to  observa¬ 
tions  made  by  Dr.  F.  T.  McLean,  July  6  and  7,  1922,  the  average  width  of 
slits  stomata  in  the  number  of  readings  indicated  was  as  shown  in  table  5. 


Table  5. 


Time. 

No.  of 
readings. 

Width  in 
microns. 

Remarks. 

4h00m  a.m. 

75 

1.0 

6  15  a.m. 

25 

1.0 

8  25  a.m. 

135 

1.8 

Widening  of  slit  begun. 

12.00  noon 

50 

2.2 

Widening  of  slit  still  in  progress. 

2  35  p.m. 

50 

2.8 

Widening  of  slit  still  in  progress. 

6  35  p.m. 

50 

1.0 

Closure  since  previous  observation. 

The  temperature  of  the  external  layer  of  wood  of  a  Monterey  pine  has 
not  been  seen  to  vary  as  much  as  10°  C.  in  a  day.  At  a  distance  of  10  cm. 
from  the  surface  the  variation  is  not  more  than  a  third  of  this  amount  at 
the  maximum  variation.  The  warming  effect  of  the  morning  sun  would 
tend  to  cause  an  expansion  of  the  trunk.  In  actuality,  the  trunk  shows  a 
shrinkage  which  begins  at  sunrise  when  the  temperature  of  the  trunk  is  at 
the  minimum  for  the  day  or  within  a  degree  of  it. 

It  seems  clear,  therefore,  that  the  daily  equalizing  variations  which  take 
place  in  a  tree-trunk  are  not  due  to  direct  water-loss  from  its  surface, 
whether  it  be  inactive  or  enlarging,  and  such  changes  are  the  reverse  of 
what  might  be  expected  as  direct  reactions  to  temperature. 

Of  the  materials  in  the  growing  layers  or  in  the  wood  which  might 
undergo  reductions  or  increases  of  sufficient  magnitude  to  alter  the  dimen¬ 
sions  of  the  trunk,  water  is  the  one  component  to  which  attention  may  be 


EXPERIMENTAL  INVESTIGATIONS. 


37 


profitably  directed.  This  liquid  is  present  as  the  hydrating  or  swelling 
agent  in  both  the  soft  cell-masses  of  the  cambium  and  bast  as  well  as  in  the 
more  rigid  walls  of  the  wood.  The  living  cells  of  the  growing  layers  will, 
of  course,  swell  and  shrink  with  the  hydration  and  dehydration  of  the 
colloids  which  form  the  bulk  of  the  protoplasm. 

The  water  in  the  woody  cells  saturates  the  walls  and  fills  the  cavities, 
especially  in  the  outer  layers,  in  which  the  greatest  change  was  found  to 
take  place.  The  watery  solution  begins  with  the  surfaces  of  the  absorbing 
organs  in  the  root-system  and  extends  as  a  continuous  system  to  the 
evaporating  surfaces  in  the  loose  tissues  of  the  leaf.  The  cohesion  tensions 
present  are  such,  according  to  various  observers,  that  any  pull  on  the  upper 
end  of  the  system  would  result  in  an  attenuation  of  the  column.  Bode1  has 
found  that  the  diameter  of  a  single  vessel  undergoes  a  measurable  reduction 
as  a  result  of  the  action  of  transpiration  on  the  cohesion  tension  of  the 
water-content.  The  irregular  column  of  water  in  a  tree-trunk  which  would 
extend  upward  principally  through  two  or  three  layers  would  be  subject  to 
such  contractions. 

STANDARDIZATION  OF  THE  DENDROGRAPH  FOR  MEASURE¬ 
MENT  OF  DAILY  EQUALIZING  VARIATIONS. 

The  measures  that  were  taken  to  standardize  the  dendrographic  apparatus 
to  avoid  errors  in  the  observations  which  might  confuse  or  obscure  the 
nature  of  the  daily  variations  should  be  described  at  this  time. 

The  essential  feature  of  the  instrument  is  a  rigid  metal  frame  surround¬ 
ing  the  trunk,  with  one  fixed  contact-point,  and  the  second  consisting  of 
the  short  bearing-arm  of  a  lever,  the  long  arm  of  which  carries  a  pen  which 
traces  the  record.  The  higher  temperatures  of  the  daytime  would  tend  to 
enlarge  this  frame,  and  if  the  tree  remained  unchanged,  or  nearly  so,  by 
reason  of  its  much  more  slowly  changing  temperature,  the  record  would 
show  an  apparent  shrinkage  if  the  floating  frame  were  made  of  iron.  To 
lessen  such  an  error,  the  floating  frames  have  been  constructed  in  some 
cases  of  “bario,”  in  others  of  “invar,”  and  in  others  of  “permant.”  The 
temperature  coefficients  of  these  alloys  are  well  known  to  be  small  and 
much  less  than  that  of  platinum;  so  small,  in  fact,  that  the  error  which 
might  be  produced  would  be  equalized  by  the  coincident  expansion  of  the 
tree.  It  was,  however,  deemed  desirable  to  ascertain  what  possible  error 
might  lurk  in  the  instrument  or  arise  from  the  mechanical  arrangement 
of  its  parts. 

A  testing-set  to  determine  the  instrumental  error  which  might  be  ascribed 
to  the  daily  fluctuations  in  sunlight  and  air  temperatures  was  arranged  as 
follows:  A  base  of  blocks,  such  as  that  which  ordinarily  serves  as  a  support 
to  a  dendrograph  when  employed  in  measuring  a  tree,  was  clasped  around 
a  short  section  of  a  trunk  of  the  Monterey  pine  set  upright  in  the  open.  A 
rod  of  fused  silica  was  laid  across  the  top  end  of  the  log  in  wooden  saddles 
which  raised  it  a  few  centimeters  above  the  surface.  A  floating  frame  of 
permant  bars  25  cm.  long  was  arranged  as  if  to  inclose  a  tree-trunk,  and 
properly  supported  on  flexible  wire  fingers.  The  contact-screw  of  the  float- 

1  H.  R.  Bode.  Beitrage  zur  Dynamik  der  Wasserbewegung  in  den  Gefasspflanzen.  Jahrb.  f. 
Wiss.  Bot.,  62,  92-127.  1923. 


38 


DENDROGRAPHIC  MEASUREMENTS. 


ing  frame  and  the  bearing-rod  of  the  lever  set  were  now  brought  into 
bearing  on  the  opposite  ends  of  a  rod  of  fused  silica  representing  the  diam¬ 
eter  of  a  tree.  The  system  represented  by  this  rod  and  the  smaller  rod  of 
fused  silica  of  the  lever  set  had  a  length  of  52  cm.  The  two  pairs  of  permant 
bars  which  formed  the  side  members  of  the  floating  frame  each  had  a  length 
of  50  cm.  If  the  silica  rod  did  not  change  in  length  and  the  permant  frame 
did  not  alter  its  dimensions  the  pen  would  trace  a  straight  line  on  the 
recording  cylinder  (fig.  4). 


Fig.  4. — Dendrograph  set  on  end  of  section  of  tree-trunk  to  test  coefficient  of  temperature- 
expansion  of  floating  frame  of  permant.  The  supporting  belt  of  blocks  encircles  the  trunk 
near  its  end,  the  members  of  the  floating  frame,  A,  A,  A,  A,  A,  being  held  in  place  in  the 
usual  manner.  A  rod  of  fused  silica,  B,  is  placed  between  the  bearing  rod  on  right-hand 
end  of  sliding  rod,  B',  of  fused  silica  on  left.  This  rod  would  represent  the  wood  in  diam¬ 
eter  of  trunk,  the  variations  of  which  would  be  recorded  in  ordinary  practice.  As  the 
variation  of  the  fused  silica  rods  is  so  small  as  to  be  negligible,  any  variation  recorded 
would  be  that  of  the  floating  frame.  C,  bars  of  permant  laid  against  bulb  of  ther¬ 
mometer. 


In  order  to  determine  what  changes  in  temperature  took  place  in  the 
members  of  the  floating  frame,  the  bulb  of  a  mercurial  thermometer  was 
held  between  two  permant  bars  by  a  rubber  band  and  laid  in  a  horizontal 
position  on  the  end  of  the  trunk.  These  bars,  like  the  members  of  the  frame, 
were  in  a  horizontal  position  and  hence  would  be  exposed  to  the  action  of 
the  sun  in  the  same  manner.  In  actual  practice  not  more  than  three-fifths 
of  the  floating  frame  would  be  exposed  to  the  sun  at  any  time,  but  here  it 


EXPERIMENTAL  INVESTIGATIONS. 


39 


was  all  exposed,  so  that  the  error  calculated  below  would  be  greater  than 
that  encountered  in  practice.  Furthermore,  it  was  assumed  that  the  fused 
silica  assumed  a  temperature  equivalent  to  that  of  the  metal,  which  is  prob¬ 
ably  not  correct;  but  here  again  the  discrepancy  would  tend  to  exaggerate 
the  error.  The  metal  of  the  floating  frame  was  found  to  range  from  10°  to 
40°  C.  on  a  warm  day  at  Carmel.  The  pen-tracing  showed  a  deviation 
from  a  straight  line  of  less  than  1  mm.  with  an  amplification  of  18  in 
the  lever  set.  Briefly  put,  no  deviation  greater  than  0.05  mm.  in  the  record 
could  be  attributed  to  the  error  of  the  instrument  under  the  test  conditions. 
The  actual  error  in  practice  would  be,  of  course,  only  a  fraction  of  this 
amount. 

The  deviation  as  given  above  represented  the  difference  between  the 
expansion  of  the  systems  of  two  fused  silica  rods  with  a  total  length  of 
52  cm.  and  the  two  pairs  of  permant  bars  with  a  length  of  50  cm.  The 
coefficient  of  expansion  of  fused  silica  through  the  ranges  of  temperature 
indicated  is  0.00000042,  from  which  it  may  be  found  by  calculation  that 
the  expansion  of  the  fused  silica  in  the  test  would  be  no  more  than  0.00063 
mm.  The  coefficient  of  expansion  of  the  permant,  which  is  a  nickel-steel 
alloy,  with  a  probable  higher  proportion  of  nickel  than  is  used  in  the  com¬ 
position  of  invar,  was  found  to  be  0.0000035  by  Professor  E.  P.  Lewis  in 
determinations  made  in  the  physical  laboratories  of  the  University  of  Cali¬ 
fornia.  The  expansion  of  invar  is  expressed  by  the  coefficient  0.0000007,  so 
that  permant  is  seen  to  show  5  times  as  much  expansion  as  invar,  or  about 
two-fifths  that  of  platinum.  The  maximum  elongation  of  the  main  axis 
of  the  floating  frame  constructed  of  permant  which  was  used  in  the  testing- 
set  would  be  0.055  mm.,  which  would  constitute  a  variation  of  about  1  part 
in  9,000  of  the  diameter  of  a  tree  which  might  be  inclosed. 

All  of  the  experiments  in  which  the  daily  equalizing  variations  were  mea¬ 
sured  exactly  were  made  with  floating  frames  of  invar  in  which  the  instru¬ 
mental  error  would  be  less  than  that  with  permant.  A  floating  frame  of 
fused  silica  wras  used  in  the  measurement  of  Monterey  pine  No.  4,  and  even 
this  small  error  was  eliminated  in  this  case. 

COURSE  OF  THE  DAILY  EQUALIZING  VARIATIONS  IN  TREES. 

Early  in  the  course  of  the  investigation  it  became  apparent  that  the 
character  of  the  reversible  variations  in  the  volume  of  a  tree-trunk  or  of 
any  other  organ  might  vary  according  to  the  stage  of  growth  or  develop¬ 
ment,  the  advance  of  the  season,  or  by  the  temperature,  relative  humidity, 
sunlight,  and  other  complexes. 

Furthermore,  as  might  be  expected,  not  all  parts  of  the  trunk  of  a  tree 
contract  and  expand  equally.  The  earlier  measurements  gave  an  apparent 
greater  variation  in  the  upper  part  of  the  trunk  than  in  the  lower.  To  con¬ 
firm  this  the  two  instruments  on  Monterey  pine  No.  1  were  calibrated  to 
give  duplicate  amplifications  in  October  1922.  On  the  warm  autumnal  days 
of  the  latter  part  of  that  month  the  absolute  variation  of  the  upper  place 
(8  meters  above  the  lower  one)  was  25  per  cent  greater  than  at  the  base  of 
the  trunk.  Thus,  on  November  1  the  recording-pen  of  the  instrument  at  the 
base  of  the  tree  stood  3  mm.  lower  on  the  sheet  at  2  p.m.  than  at  9  a.m. 
The  instrument  at  the  upper  place  on  the  same  trunk  moved  the  recording 


40 


DENDROGRAPHIC  MEASUREMENTS. 


pen  4  mm.  lower  in  the  afternoon,  the  diameter  here  being  37  cm.  and  the- 
amplification  being  10  in  both  instruments.  The  diameter  of  the  trunk  had 
therefore  shrunk  0.3  mm.  at  the  base  and  0.4  mm.  in  the  upper  part.  The 
upper  part  of  the  trunk  was  but  370  mm.  in  diameter,  and  the  coefficient  of 
expansion  was  thus  seen  to  be  1  part  in  900.  The  lower  part  of  the  trunk 
had  a  diameter  of  500  mm.  and  consequently  a  coefficient  of  expansion  of 
about  1  part  in  1,700,  or  less  than  six-tenths  that  of  the  upper  part  of  the 
trunk. 

This  behavior  of  the  woody  trunk  is  to  be  compared  with  that  of  the 
heavier  thickened  roots  a  short  distance  away  from  the  base  of  the  trunk. 
Some  description  of  the  behavior  of  these  members  has  already  been  given.. 
Late  in  June  a  root  which  was  40  mm.  in  thickness  was  showing  a 
daily  variation  of  1  part  in  364,  which,  of  course,  included  the  cambium 
layer.  The  most  notable  fact  concerning  this  matter  is  that  the  root  exhibits 
a  daily  cycle  notably  different  from  that  of  the  stem  in  that  it  begins  to 
enlarge  shortly  after  midday,  while  the  expansion  of  the  stem  does  not 
commence  until  3,  4,  or  5  hours  later.  Also  that  the  root  begins  to  contract 
before  midnight  at  a  time  when  the  entire  system  of  the  tree  must  be  in  a 
condition  most  nearly  approaching  satisfaction  as  to  hydration. 

The  more  complete  picture,  then,  of  a  massive  tree  brings  into  focus  the 
fact  that  the  trunk  of  the  Monterey  pine  contracts  during  the  daylight 
period,  in  which  the  stomatal  slits  and  the  resultant  transpiration  are 
greatest,  that  the  contraction  is  greatest  in  the  upper  part  of  the  trunk,  and 
that  the  roots  begin  to  enlarge  about  the  time  the  stems  have  reached  their 
minimum  volume  and  many  hours  before  they  begin  to  expand. 

The  variations  in  the  trunk  seem  to  be  invariably  and  closely  connected 
with  the  transpiratory  activity  of  the  leaves.  Extreme  reduction  of  tran¬ 
spiration  by  removal  of  the  leaves  or  disconnection  with  the  water-supply 
are  followed  by  a  lessened  amplitude  of  variation.  The  daily  variation 
was  reduced  to  a  minimum  in  a  tree  defoliated  early  in  the  growing-season, 
with  only  half-formed  young  leaves  remaining;  on  the  other  hand,  the  daily 
change  was  very  marked  in  a  tree  defoliated  in  midsummer,  with  the  newly 
formed  leaves  nearly  mature,  and  probably  having  a  transpiratory  capacity 
equivalent  to  the  amount  taken  in  from  the  roots  from  a  slowly  drying 
soil.  The  variation  was  lacking  for  a  few  days  in  a  tree  girdled  above  the 
dendrograph,  the  girdle  being  callused  later  with  a  resumption  of  the 
variation.  Girdling  near  the  base  of  the  tree  early  in  the  season  had  no 
direct  effect  on  the  variation  during  that  year,  but  its  amplitude  was  much 
reduced  in  the  following  season  preceding  the  death  of  the  tree  in  mid¬ 
summer.  The  variation  quickly  disappeared  from  a  tree  topped  below  all 
of  the  branches,  was  much  reduced  in  a  tree  topped  with  only  a  few  branches 
remaining,  and  was  not  visibly  affected  in  a  tree  in  which  topping  removed 
about  half  of  a  tree  which  was  densely  branched  and  with  ample  foliage 
remaining.  The  variation  disappeared  within  10  days  from  a  tree,  the  base 
of  which  had  been  killed  by  boiling  oil. 

That  the  daily  variation  depends  chiefly  upon  the  transpirational  rela-  • 
tions  seems  obvious  from  its  seasonal  aspects.  In  a  young  tree,  such  as 
No.  17,  contraction  does  not  begin  until  8  a.m.  in  the  autumn  and  winter, . 


EXPERIMENTAL  INVESTIGATIONS. 


41 


and  expansion  is  in  evidence  by  3  p.m.  As  soil-moisture  and  relative 
humidity  increase  with  the  winter  rains  and  the  activity  of  the  guard-cells 
is  lessened  by  low  temperatures,  the  contraction  is  lessened  and  the  period 
of  lessening  volume  is  shortened,  until  about  January  1  it  does  not  begin 
until  10  a.m.  and  expansion  is  visible  by  2  p.m.  The  contraction  is  more 
abrupt  than  the  expansion  in  any  case,  and  during  the  entire  year.  Thus, 
in  January,  contraction  is  complete  in  4  or  5  hours,  while  expansion  may 
extend  over  16  or  even  18  hours.  The  greatest  amplitude  of  the  variation 
in  this  tree  was  0.4  mm.  daily  during  the  latter  part  of  March  and  on  warm 
days  favoring  transpiration.  The  least  change  was  on  rainy  or  foggy  days 
and  wras  seen  in  July  and  August,  at  a  time  when  the  trunk  was  in  a  con¬ 
dition  of  rapid  enlargement.  It  is  withal  somewhat  remarkable  that  the 
variation  should  be  less  at  this  time  than  in  the  cool,  rainy  season  of 
December  and  January.  The  greatest  coefficient  of  expansion  of  the  entire 
trunk,  including  the  green  bark  which  had  not  begun  to  flake  and  had  a 
diameter  over  all  of  160  mm.,  was  thus  seen  to  be  1  in  400. 

The  generalizations  as  noted  above  also  apply  to  an  older  tree,  No.  1, 
which  was  about  50  cm.  in  diameter  at  the  base.  The  maximum  variation 
daily  in  early  April  was  0.4  mm.,  which  would  be  1  part  in  1,250.  The  vari¬ 
ation  at  a  place  8  meters  higher  on  the  stem  at  this  time  was  over  0.5  mm., 
which  was  1  part  in  700.  It  seems  probable  that  the  terminal  part  of  the 
trunk  would  at  a  corresponding  diameter  have  a  coefficient  of  expansion 
equivalent  to  that  of  the  basal  part  of  a  young  tree.  The  amplitude  of  the 
expansion  may  depend  upon  some  condition  of  the  wood  which  may  not  be 
defined,  except  to  say  that  the  outer  layers,  through  which  liquids  chiefly 
move,  may  show  greater  changes  than  the  heart  and  inner  layers.  Some 
results  as  to  the  daily  variations  of  the  woody  cylinder  have  already  been 
published.  The  measurements  were  repeated  and  extended  with  an  older 
tree. 

DAILY  VARIATIONS  IN  THE  VOLUME  OF  THE  INNER  WOODY 
CYLINDER  OF  A  MONTEREY  PINE  TREE. 

An  instrument  of  the  new  design  was  fitted  on  Monterey  pine  No.  4, 
which  had  been  the  subject  of  the  earliest  measurements  made  in  September 
1918.  The  present  measurements  were  to  be  concerned  with  the  variations 
in  the  wroody  cylinder  only.  On  April  7,  1922,  the  layer  formed  during  that 
season,  as  well  as  the  wood  formed  in  1921,  was  removed  over  a  small 
circular  area  about  3  to  4  cm.  across  to  allow  the  contact  screw  and  the 
silica  rod  of  the  lever-set  to  rest  on  the  wood  of  1920.  The  diameter 
between  the  two  points  was  about  42  cm.  The  first  floating  frame  was  of 
bario,  a  second  one  of  fused  silica  was  substituted  later,  and  finally  one  of 
permant,  the  consistent  action  of  the  tree  in  all  three  settings  giving  assur¬ 
ance  that  the  variations  described  below  are  mainly  of  the  woody  cylinder 
and  are  not  due  to  instrumental  errors.  This  feature  of  the  matter  has  been 
discussed  on  a  preceding  page. 

The  daily  change  in  diameter  amounted  to  0.13  mm.  in  April,  and  this 
increased  to  0.17  late  in  June,  and  fluctuations  of  this  amplitude  continued 
until  late  in  July,  at  which  time  the  soil-moisture  would  begin  to  fall  away 
notably  and  the  transpiration  reach  a  maximum.  The  next  feature  was 


42 


DENDROGRAPHIC  MEASUREMENTS. 


that  of  the  slow  recovery  following  the  daily  contraction.  Beginning  of 
recovery  set  in  shortly  after  noon  in  April  and  May;  with  the  advance  of 
the  season  recovery  was  belated,  until  in  September  the  enlargement  was 
not  noticeable  until  5  or  6  p.m.,  although  the  actual  amplitude  of  the  change 
was  lessening,  being  at  this  time  no  greater  than  in  April.  The  amplitude 
again  increased  in  October  and  November  until  it  was  equivalent  to  that 
of  June,  the  fluctuation  being  characterized  by  the  abrupt  contraction  in 
which  the  full  shrinkage  was  reached  within  two  hours. 

Some  question  as  to  the  contacts  of  the  instruments  in  January  and 
February  are  allowable,  so  the  record  for  this  period  is  to  be  disregarded. 
Perfected  adjustments  were  made  on  March  9.  It  is  to  be  noted  that  now 
the  wood  of  1920,  on  which  the  contacts  were  made,  was  overlaid  by  that 
of  1921  and  1922  on  the  entire  part  of  the  trunk,  and  the  layer  of  1920 
probably  represents  the  innermost  layer  in  which  transport  of  solutions 
takes  place  in  any  notable  volume. 

The  daily  change  in  March  was  slightly  less  than  0.2  mm.  and  may  be 
taken  to  be  about  equivalent  to  that  found  in  April  in  the  preceding  year 
and  also  in  April  and  May  of  this  year.  Decrease  in  variation  continued 
until  in  the  week  beginning  September  10,  1923.  The  record  was  a  direct 
line,  and  the  departure  was  probably  not  more  than  a  fifth  of  the  maximum, 
and,  therefore,  not  to  be  estimated  with  any  profitable  degree  of  accuracy. 
The  contraction  was  abrupt  and  the  recovery  slow,  as  in  the  measurements 
of  the  entire  trunk,  and  the  course  of  the  fluctuations  is  seen  to  follow  that 
of  the  entire  trunk. 

The  maximum  coefficient  of  expansion  would  be  about  1  part  in  2,000. 
This  figure  is  to  be  compared  to  the  ones  obtained  from  a  smaller  tree 
measured  in  1920,  in  which  the  maximum  contraction  was  estimated  at  1 
part  in  1,750  and  the  minimum  at  1  part  in  8,750,  there  being  obvious 
agreement. 

The  woody  cylinder  of  the  tree  last  measured  may  be  compared  directly 
with  that  of  the  trunk  of  No.  1,  which  is  slightly  larger  but  probably  about 
the  same  age.  The  ratio  of  expansion  of  the  entire  trunk  of  No.  1,  as 
described  on  the  previous  page,  had  a  maximum  of  1  part  in  1,250,  which 
would  indicate  that  the  outer  layers  of  wood  and  the  bast  and  cortex  have 
a  higher  coefficient  of  expansion  than  that  of  the  woody  cylinder,  as  might 
be  reasonably  expected. 

GROWTH  OF  THE  ARIZONA  PINE. 

Dendrographs  were  attached  to  the  trunks  of  two  Arizona  pines  ( Pinus 
arizonica),  growing  at  8,000  feet  in  the  Santa  Catalina  Mountains  in  south¬ 
ern  Arizona,  on  March  24,  1922.  No.  1  was  near  the  bottom  of  a  small 
lateral  stream  valley  sloping  to  the  northward,  with  an  apparent  good 
supply  of  soil  moisture.  The  trunk  was  18  cm.  in  diameter;  the  tips  of 
the  branches  had  begun  to  elongate,  but  the  bast  and  cambium  were 
apparently  inactive.  The  lever  of  the  recorder  was  set  to  amplify  the 
variation  in  the  trunk  18  times.  By  means  of  a  thermometer  inserted  under¬ 
neath  the  bark  it  was  seen  that  the  growing  layer  was  subject  at  this  time 
to  temperatures  as  low  as  13°  C.  Growth  began  on  June  2  and  continued 
until  July  9,  when  a  short  period  of  warm  weather  was  accompanied  by 


EXPERIMENTAL  INVESTIGATIONS. 


43 


great  daily  equalizing  variations  with  no  net  increase.  On  July  18  the 
summer  rains  began,  the  daily  variations  were  reduced  to  a  minimum,  and 
some  enlargement  followed  which  had  definitely  come  to  an  end  by  Sep¬ 
tember  1,  with  the  season  of  growth  being  included  in  a  period  of  90  days. 
During  this  time  the  pen  of  the  recorder  had  moved  upward  over  23  mm. 
on  the  series  of  recording  sheets,  indicating  a  total  increase  of  1.2  mm.  in 
thickness.  The  temperature  of  the  cambium  layer  had  varied  between 
13°  and  19°  C.  during  this  time. 

The  rate  of  growth  had  not  been  widely  different  from  that  noted  in  the 
previous  20  years,  the  age  of  the  tree  being  about  55  to  60  years. 

Tree  No.  2  of  this  species  was  about  200  meters  distant,  on  the  south¬ 
facing  slope  of  the  main  valley.  The  substratum  was  coarse,  granular 
granite,  in  which  the  water-supply  would  be  very  limited.  The  exposure 
to  the  sun  was  such  as  to  induce  a  maximum  transpiration.  The  tips  of 
the  branches  were  beginning  to  elongate  when  the  instrument  was  attached 
on  May  24,  and  the  dendrograph  recorder  was  set  to  amplify  variations  18 
times.  No  enlargement  could  be  detected  until  June  10,  when  an  irregular 
increase  began  with  very  marked  daily  variations.  No  net  increase  could 
be  detected  between  July  9  and  July  18,  in  agreement  with  the  behavior  of 
No.  1  in  response  to  the  hot  and  dry  weather.  Temperatures  of  30°  and 
31°  C.  of  the  cambium  were  noted.  The  beginning  of  the  summer  rains 
was  followed  by  a  renewed  enlargement;  which  continued  until  September  6. 
The  period  from  the  beginning  of  growth  until  its  end  included  88  days.  The 
recording-pen  moved  upward  over  32  mm.  spaces  of  the  sheet,  indicating  an 
enlargement  of  about  1.8  mm.  in  diameter.  This  tree  had  shown  a  slightly 
greater  growth-rate  during  its  lifetime  than  during  the  present  year,  its  age 
being  not  widely  different  from  that  of  No.  1.  The  annual  rings  indicated 
an  age  of  65  to  70  years.  The  location  is  one  which  may  be  taken  to  be  at 
the  upper  range  of  altitude  of  this  tree.  This  being  the  case,  No.  1  with  its 
northern  exposure  was  under  conditions  farther  from  the  optimum  than 
No.  2. 


THE  MEXICAN  WHITE  PINE. 

The  dendrograph  was  attached  to  the  trunk  of  a  Pinus  strobiformis  35 
cm.  in  diameter,  which  stood  midway  between  the  two  trees  of  Arizona  pine, 
the  activities  of  which  have  been  described  above.  The  soil  conditions 
seemed  favorable  for  an  adequate  water-supply.  The  dendrograph  recorder 
was  set  to  give  an  amplification  of  20  times.  The  tips  of  the  branches  w^ere 
beginning  to  elongate  on  May  24,  when  the  record  was  begun. 

Growth  began  about  June  6  or  7,  but  in  a  period  beginning  July  5  and 
lasting  until  July  17  no  net  enlargement  was  made.  A  second  impulse  of 
growth  was  shown  which  ended  August  10,  the  total  period  in  which  growth 
took  place  thus  being  65  days. 

The  recording-pen  moved  upward  over  32  mm.  intervals  and  the  net 
increase  was  therefore  about  1.6  mm.  This  would  represent  about  the 
average  increase  for  many  years.  The  borings  taken  from  the  trunk  did 
not  reach  the  center  of  the  tree,  which  must  have  reached  an  age  well  over 
a  century. 


44 


DENDROGRAPHIC  MEASUREMENTS. 


RELATION  OF  THE  ARIZONA,  MEXICAN,  AND  CHIHUAHUA 

PINES  TO  SEASONAL  VARIATIONS. 

The  Mexican  white  pine  ( Pinus  strobiformis )  growing  near  the  Arizona 
pines  was  also  seen  to  show  some  activity  early  in  June,  after  which  a 
period  of  no  increase  followed.  Actual  enlargement  began  in  mid-July, 
following  the  occurrence  of  the  summer  rains  on  the  Santa  Catalina  Moun¬ 
tains,  in  which  these  pines  were  growing  at  an  elevation  of  about  7,000  feet. 
The  period  from  the  beginning  of  growth  to  its  end  was  inclusive  of  only 
65  days.  Growth  was  manifest  on  only  53  days.  A  Chihuahua  pine  ( Pinus 
chihuahuensis)  at  a  little  over  6,000  feet  showed  some  enlargement  in  a 
period  of  about  10  days  beginning  April  13,  1919,  with  a  similar  slight 
impulse  a  month  later.  A  third  slight  increase  took  place  in  a  few  days 
at  the  end  of  May.  The  main  part  of  the  formation  of  wood  for  the  season 
began  on  July  20,  three  weeks  after  the  summer  rains  had  begun.  This 
period  terminated  August  23.  A  final  brief  period  of  increase  occurred 
from  September  14  to  October  5.  The  time  from  the  manifestation  of  the 
first  enlargement  to  the  end  of  the  season  was  174  days,  but  during  this 
time  the  tree  showed  only  active  increase  on  about  80  days.  (Growth  in 
trees,  Carnegie  Inst.  Wash.,  Pub.  No.  307,  1921,  pp.  28  and  29.) 

The  studies  of  the  Arizona,  Mexican,  and  Chihuahua  pines  were  made 
on  trees  on  the  Santa  Catalina  Mountains,  near  Tucson,  Arizona.  These 
mountains  are  an  “island”  range  in  a  region  of  aridity.  The  precipitation 
takes  place  in  two  periods,  midsummer  and  midwinter  in  about  equal  pro¬ 
portions.  That  for  three  summer  seasons,  as  furnished  by  the  Forest 
Service,  is  from  instruments  which  were  installed  within  a  short  distance 
of  the  Arizona  pines  upon  which  the  observations  were  carried  out  (table  6). 


Table  6. — Summer  rainfall  in  the  pine  forest,  at  8,000  feet,  Santa  Catalina 

Mountains,  Arizona. 


1921. 

1922. 

1923. 

inches. 

inches. 

inches. 

May . 

0.0 

0.11 

0.24 

June . 

0.88 

1.19 

0.00 

July . 

15.79 

7.93 

August . 

8.22 

19.25 

6.54 

Total  in  season  affecting  growth . 

24.89 

20.55 

14.47 

The  advance  of  temperatures  in  May  and  June  is  accompanied  by  a  pro¬ 
gressive  reduction  of  the  soil-moisture  content,  the  whole  surface  layer  with 
the  humus  becoming  so  dry  before  the  tropical  rains  of  midsummer  that 
many  great  fires  occur  in  the  forest  at  this  time.  This  condition  is  such 
that  when  the  soil  and  air  temperatures  are  high  enough  for  growth  water 
is  lacking  and  the  relative  humidity  is  very  low.  To  such  extremes  have 
these  conditions  gone  that  growth  does  not  begin  until  2  or  3  weeks  after 
the  coming  of  the  summer  rains.  Some  time  is  necessary  for  the  water  of 
the  rains  to  percolate  to  the  depths  at  which  the  absorbing  roots  are  placed, 
and  further  time  is  necessary  for  this  water  to  enter  the  roots  and  ascend 
the  stems  to  the  cambium  layers. 


EXPERIMENTAL  INVESTIGATIONS. 


45 


The  behavior  of  the  trees  of  which  dendrographic  records  have  been 
made  suggests  that  it  is  not  to  be  assumed  that  the  thickness  of  the  layers 
of  the  wood  on  a  trunk  is  a  reliable  index  of  the  relative  amount  of  pre¬ 
cipitation  of  the  season  in  which  the  wood  is  formed.  It  has  been  found 
that  this  is  so  in  the  case  of  the  Monterey  pine,  and  it  may,  therefore,  not 
be  taken  for  granted  in  the  case  of  any  species  until  confirmed  by  actual 
measurements  for  a  term  of  years. 

This  is  also  suggested  by  facts  recently  uncovered  in  the  Santa  Catalina 
Mountains  in  Arizona,  the  habitat  of  the  Arizona  and  Mexican  pine.  The 
dendrographic  records  of  these  two  pines  and  the  examination  of  cores 
taken  by  the  increment  borer  showed  that  the  layer  of  wood  formed  in 
1922  did  not  differ  markedly  from  that  of  previous  years,  although  the 
rainfall,  which  might  have  been  effective  in  promoting  growth  in  1921,  was 
about  as  25  to  20.5  in  1922.  During  the  preceding  years,  including  1922, 
the  layers  had  a  thickness  of  1.2  to  1.8  mm.  Some  cores  were  taken  by  the 
increment  borer  in  September  1923;  the  layer  formed  in  the  summer 
season  then  closing  was  double  that  of  previous  years,  and  was  greater 
than  that  of  other  layers,  except  in  the  part  of  the  tree  formed  while  young. 

Now,  the  summer  season  of  1923,  in  the  habitat  of  these  pines,  was 
characterized  by  the  lowest  rainfall  of  any  since  the  record  had  been  taken, 
14.47  as  compared  to  19.25  in  1922,  and  10.21  as  measured  at  the  Desert 
Laboratory.  Upon  consultation  with  a  number  of  people  who  have  spent 
many  summers  in  camp  in  the  forested  area  of  the  mountains,  I  found 
the  general  impression  to  be  that  the  summer  of  1923  was  one  of  great- 
cloudiness  and  continued  high  humidity  and  dampness,  and  the  impression 
also  prevailed  in  consonance  with  the  records  that  the  rainfall  had  been 
moderate  or  below  the  average.  Unfortunately,  no  records  of  the  evapora¬ 
tion  had  been  taken  for  several  years.  In  view  of  the  fact  that  the  rainfall 
totals  do  not  correspond  with  the  thickness  of  the  woody  layers  formed 
on  the  pines  in  the  Santa  Catalina  Mountains,  it  must  be  decided  that 
these,  as  in  the  Monterey  pine,  may  not  be  held  as  reliable  indices  of  the 
precipitation  factor  in  climate.  The  facts  noted  above,  however,  do  suggest 
that  pines  which,  like  P.  arizonica,  P.  chihuahuaensis ,  P.  scopalorum,  P. 
strobiformis,  and  perhaps  P.  ponderosa,  inhabit  regions  in  which  the 
beginning  and  end  of  the  growing-season  seems  to  be  determined  by  the 
percentage  of  soil  moisture  resulting  from  the  precipitation  of  the  current 
season,  are  in  a  critical  condition  with  respect  to  this  feature  and  to  relative 
humidity  as  largely  determined  or  accompanying  cloudiness.  Extension  of 
the  growing-season  by  earlier  or  later  rains  might  reasonably  be  expected  to 
show  in  the  layers  of  wood,  although  the  occurrence  of  early  rains  in  1922 
did  not  show  such  direct  effect.  A  favorable  season  would  be  one  in  which 
the  soil  moisture  would  be  adequate,  the  temperature  range  within  the 
limits  of  growth,  and  the  illumination  sufficient  for  photosynthesis,  while 
the  relative  humidity  would  be  such  as  to  prevent  excessive  transpiration. 
In  the  case  of  the  pines  on  the  Santa  Catalina  Mountains,  all  of  the  condi¬ 
tions  seem  to  range  within  favorable  limits  during  July  and  August,  except 
relative  humidity.  When  that  feature  is  increased  by  cloudiness,  maximum 
wood-formation  takes  place. 


46 


DENDROGRAPHIC  MEASUREMENTS. 


THE  YELLOW  PINE. 

A  dendrograph  of  an  old  design  was  attached  to  a  yellow  pine  ( Pinus 
scopulorum )  near  the  forest  experiment  station  in  Fort  Valley,  near  Flag¬ 
staff,  Arizona,  in  the  summer  of  1920.  The  instrument  was  set  to  give  a 
small  amplification  and  the  tree  was  nearly  quiescent  during  the  season, 
with  the  result  that  the  records  were  indeterminate. 

Instruments  were  attached  to  two  trees  near  the  same  place  on  May  14, 
1923,  and  the  adjustments  were  made  to  give  amplifications  of  14  for  No.  1 
and  18  for  No.  2.  The  location  is  at  an  elevation  of  over  7,000  feet,  the  soil 
is  volcanic,  and  the  rainfall  total  has  an  average  of  23  inches.  About  40 
per  cent  of  this  comes  in  the  winter  and  most  of  the  remainder  falls  during 
the  summer  thunder-storms.  Both  trees  were  in  the  inclosure  of  the  build¬ 
ings  of  the  station  and  the  observations  were  carried  out  personally  by 
Mr.  G.  A.  Pearson,  who  has  been  in  charge  of  the  station  for  15  years. 

Tree  No.  1  was  about  40  cm.  (15.8  inches)  in  diameter,  being  still  in  a 
condition  in  which  the  elongation  of  the  main  stem  was  proceeding  vigor¬ 
ously.  No  enlargement  of  the  trunk  was  visible  until  June  1,  which  was 
two  weeks  later  than  No.  2,  which  stood  only  400  feet  away  but  was  much 
younger.  The  daily  equalizing  variation  at  the  time  of  beginning  growth 
was  about  0.3  mm.  daily,  which  amount  sustains  a  much  smaller  proportion 
to  the  diameter  of  the  trunk  than  the  variation  in  No.  2.  Growth  was 
apparently  continuous  until  about  August  24.  During  this  time  the  total 
recorded  increase  in  diameter  was  about  4.5  mm.  An  examination  of  a 
sample  taken  by  the  increment  borer  from  a  place  near  the  contacts  of  the 
instruments  showed  two  opposite  layers,  2  and  2.5  mm.  thick.  The  daily 
variation  ranged  from  1  part  in  1,300  at  the  beginning  of  the  growing-season 
to  1  part  in  800  at  its  height.  This  rate  had  decreased  but  little  by  the  end 
of  August. 

Tree  No.  2  was  14  cm.  (5.4  inches)  in  diameter  at  the  height  at  which 
the  instrument  was  attached  and  was  about  14  feet  in  height.  It,  as  well 
as  No.  1,  stood  in  an  open  formation  in  which  the  amount  of  shading  was 
negligible.  At  the  time  of  the  attachment  of  the  instrument  on  May  14  the 
daily  equalizing  variation  in  the  diameter  of  the  trunk  amounted  to  about 
0.3  mm.,  or  1  part  in  450.  Some  slight  enlargement  was  noticeable  on  the 
16th,  which  continued  for  about  72  days,  with  a  total  enlargement  of  4.5 
mm.  in  diameter  in  this  time.  But  little  increase  took  place  in  the  12  days 
beginning  July  27,  but  on  August  8  the  pen  began  to  rise  in  its  course,  and 
during  the  following  week  a  further  accretion  of  about  0.5  mm.  was  made. 
After  this  the  increase  was  very  slight.  The  total  of  the  two  layers  in 
samples  from  opposite  sides  of  the  tree  was  about  6  mm.  The  daily  varia¬ 
tion  had  increased  slightly  in  the  time  of  most  rapid  growth,  amounting  to 
1  part  in  350  in  the  first  half  of  July.  The  amplitude  of  the  variations 
had  decreased  to  that  shown  at  the  beginning  of  the  season  by  the  latter 
part  of  August. 

The  period  of  enlargement  in  the  larger  tree  was  from  June  1  to  August 
24,  or  85  days  inclusive;  that  of  the  smaller  and  younger  tree  may  not  be 
determined  so  exactly.  Enlargement  began  on  May  16 ;  an  intermission  of 
12  days  was  seen  at  the  end  of  July,  and  decisive  increase  ceased  on 
August  15.  The  time  between  the  two  dates  given  would  amount  to  91  days. 


EXPERIMENTAL  INVESTIGATIONS. 


47 


The  record  of  the  growth  of  a  tree  of  Pinus  ponderosa  on  the  slopes  of 
Pike’s  Peak  in  1920  show  that  in  this  case  a  slight  growth  was  displayed  on 
June  14,  before  the  buds  awakened,  but  that  the  seasonal  enlargement  did 
not  begin  until  August  12,  and  practically  all  of  the  season’s  formation  of 
wood,  amounting  to  an  increase  in  diameter  of  2  mm.,  took  place  in  the 
period  of  23  days  following.  (See  Growth  in  trees,  Carnegie  Inst.  Wash. 
Pub.  307,  p.  29,  1921.) 

The  behavior  of  an  Arizona  pine  ( Pinus  arizonica)  in  1922  was  similar. 
A  slight  growth  impulse  was  exhibited  early  in  June,  followed  by  a  period 
in  which  only  equalizing  variations  might  be  seen,  then  in  mid-July  actual 
enlargement  of  the  trunk  began,  following  the  summer  rains,  the  periods 
from  the  first  display  of  activity  to  the  end  of  enlargement  being  88  to  90 
days. 

THE  CALIFORNIA  REDWOOD. 

Some  of  the  considerations  presented  in  the  preceding  paragraph  were 
taken  into  account  in  the  arrangement  of  dendrographic  observations  of 
Sequoia  sempervirens ,  the  California  redwood.  This  tree  finds  its  best  con¬ 
ditions  for  existence  in  the  coastal  region  of  northern  California,  where  it 
formed  dense  and  extensive  forests  in  valleys  with  gentle  slopes,  in  which 
it  extended  far  back  from  the  coast  between  latitudes  38°  to  41°  N.  South 
of  the  Bay  of  Monterey,  and  between  latitudes  36°  and  37°  N.,  the  tree  is 
found  only  in  the  deeply  cut  canons  with  steep  slopes  which  come  down 
directly  from  the  summits  of  the  Santa  Lucia  Mountains,  which  are  at  no 
place  more  than  a  few  miles  from  the  shore.  In  every  one  of  these  canons 
the  tree  extends  up  the  laterals,  actually  reaching  the  crests  at  1,600  to 
1,800  feet  in  some  cases.  These  outliers  do  not  attain  average  normal  size, 
and  groves  of  dwarfed  individuals  of  great  age  may  be  found  on  slopes 
exposed  to  the  direct  action  of  winds  from  the  sea,  which  have  some  resem¬ 
blance  to  the  wind-blown  and  stunted  trees  of  various  pines  which  char¬ 
acterize  the  timber-line  region  of  high  mountains. 

Measurement  of  redwood  trees  was  carried  on  in  Palo  Colorado  Canon 
during  1921,  1922,  and  1923.  Five  trees  in  all  were  kept  under  observation. 
All  of  these  were  about  2  miles  from  the  sea,  at  an  elevation  of  less  than 
1,000  feet,  and  at  a  point  about  12  miles  south  of  the  Coastal  Laboratory 
at  Carmel.  Furthermore,  these  trees  were  within  100  miles  of  the  extreme 
southern  limit  of  the  species. 

Tree  No.  1  stood  on  a  south-facing  slope  at  the  upper  margin  of  the  thin 
strip  of  forest  which  filled  the  canon  below.  It  was  near  the  residence  of 
Mr.  H.  B.  Vandall,  who  gave  the  information  that  it  had  come  up  near 
an  outflow  of  water  within  the  memory  of  persons  living,  and  probably  had 
an  age  of  about  30  years.  This  estimate  is  confirmed  by  a  core  taken  out 
by  an  increment  borer.  The  trunk  was  about  15  inches  in  diameter  when 
the  measurements  were  begun  in  April  1921,  and  some  basal  side-shoots 
were  cut  away  in  making  arrangements  of  the  dendrograph. 

The  floating  frame  of  bario  bars  was  first  attached  to  the  tree  on  April 
8,  1921.  The  buds  at  this  time  were  still  quiescent  on  the  uppermost 
branches,  but  those  near  the  ground,  where  they  were  less  exposed  to  the 
cool  winds  and  might  receive  radiation  from  the  ground  warmed  by  the 
sun,  showed  an  elongation  of  as  much  as  15  mm.  on  some  branches. 


48 


DENDROGRAPHIC  MEASUREMENTS. 


Increase  of  diameter,  with  marked  daily  variations,  continued  at  a  vary¬ 
ing  rate  until  October  21,  giving  a  growing  period  of  190  days.  The  total 
increase  in  diameter  was  24  mm.  The  only  actual  interruption  of  the 
upward  trend  of  the  recording-pen  was  during  a  period  of  a  few  days  of 
hot,  dry  weather  the  first  week  in  July  (fig.  5). 

The  instrument  was  taken  down  November  9.  It  was  again  put  in  place 
on  April  5,  1922.  Upward  movement  of  the  recording-pen,  marking  the 
beginning  of  the  activity  of  the  cambium,  was  shown  on  April  19.  The 
activities  of  the  buds  began  in  some  instances  before  the  dendrographic 


JUNE  20,1921 


Fig.  5. — Facsimile  of  weekly  dendrograph  records  of  redwood  No.  1.  The  beginning  of  the 
growing-season  is  seen  in  lowest  record.  The  absence  of  daily  contraction  is  recorded  in 
week  beginning  May  2,  during  a  rainy  period  of  2  days.  The  changing  character  of 
rates  of  growth  and  of  character  of  daily  variations  with  the  advance  of  the  season  is 
illustrated  by  the  other  records.  Horizontal  intervals  represent  6  hours,  and  vertical 
spaces  1  cm.  The  actual  variation  of  diameter  of  trunk  is  amplified  10  times. 

increases  were  recorded,  but  on  others  awakening  came  later.  Many 
branches  were  seen  on  May  8  which  had  recently  made  an  elongation  of 
2  to  4  cm.  The  increase  was  interrupted  for  a  period  of  a  few  days  early 
in  July  by  hot,  dry  weather,  but  the  period  of  growth  extended  to  October 
24,  and  may  thus  be  seen  to  include  a  period  of  202  days.  The  total  increase 
in  diameter  was  17  mm.,  which,  it  is  to  be  noted,  was  less  than  the  accretion 
for  1921.  The  rainfall  at  Carmel,  12  miles  to  the  northward,  was  17.5 
inches  in  the  year  terminating  in  midsummer  of  1921,  and  as  no  rainfall 
occurred  during  the  remainder  of  the  growing-season,  the  reference  to  this 
measurement  seems  pertinent.  The  slope  immediately  above  the  tree  was 
irrigated  to  some  extent,  however,  and  no  direct  connection  may  be  taken 


EXPERIMENTAL  INVESTIGATIONS. 


49 


for  granted.  The  total  amount  for  the  second  year  was  about  23  inches 
at  Carmel.  This  higher  precipitation  is  seen  to  be  associated  with  a  longer 
growing-period,  but  the  matter  of  irrigation  and  the  fact  that  the  instru¬ 
ment  used  the  first  year  was  of  a  crude  design  makes  it  unsafe  to  make 
further  comparisons. 

Basal  shoots  arise  freely  from  the  trunks  of  the  redwood,  or  from  stumps 
of  trees  which  have  been  broken  off,  cut  down,  or  prostrated  by  the  wind. 
A  large  proportion  of  the  trees  in  such  a  forest  as  that  in  Palo  Colorado 
Canon  probably  thus  arose  as  “suckers”  on  other  trees.  A  stem  of  this 
type  was  taken  as  No.  2  of  the  redwood  series.  It  had  arisen  from  the 
surface  of  a  large  root  of  another  tree  slightly  larger  than  No.  1,  but  stand¬ 
ing  only  a  few  yards  from  it.  The  main  trunk  was  50  cm.  in  diameter  and 
the  offshoot,  which  was  to  be  measured,  was  14  cm.  in  thickness. 

The  dendrograph  was  attached  on  April  3,  1922.  Daily  equalizing  vari¬ 
ations  only  were  apparent  until  June  6,  when  a  slight  enlargement  began 
which  continued  for  a  week  only,  resulting  in  an  increase  of  about  0.5  mm. 
The  trunk  of  No.  1  had  begun  growth  on  April  19  and  the  main  trunk  of 
this  one  probably  acted  in  the  same  way.  After  the  first  week  the  sucker 
showed  only  equalizing  variations  for  a  month,  beginning  to  enlarge  again 
on  July  12,  at  which  time  the  daily  variation  was  at  a  minimum. 

The  rate  of  increase  was  low  and  the  growth  which  terminated  on 
October  12  resulted  in  a  total  increase  of  but  5  mm.  The  period  from  the 
beginning  to  the  close  of  the  growing-season  was  128  days,  but  the  trunk 
was  active  on  only  100  days.  Whether  this  restriction  was  due  to  the 
stronger  competition  of  the  main  stem  for  the  supply  of  moisture  from  the 
soil  furnished  by  the  common  root-system  is  not  known,  but  it  is  a  reason¬ 
able  inference. 

The  measurements  of  redwoods  Nos.  4  and  5  were  arranged  to  test  this 
relation  of  two  trees,  one  of  which  was  borne  as  a  younger  offshoot  of  a 
large  root  of  the  other.  This  pair  stood  in  a  dense  formation  on  the  south¬ 
ward-facing  slope  of  the  canon,  in  which  the  trees  stand  so  closely  together 
that  the  direct  rays  of  the  sun  do  not  reach  the  ground  and  only  the  crowns 
of  the  trees  are  exposed  to  direct  sunlight.  This  is  in  contrast  with  Nos. 
1  and  2,  which  stood  fairly  in  the  open. 

The  offshoot,  No.  5,  had  a  trunk  which  at  a  meter  from  the  ground  had 
a  diameter  of  27  cm.,  including  the  bark.  The  bark  was  several  centimeters 
in  thickness  and  some  of  it  had  to  be  cut  away  under  the  support  in  order 
to  get  a  firm  bearing.  It  was  trimmed  away  to  a  thickness  of  a  millimeter 
under  the  bearing  points,  in  the  usual  manner.  The  record  was  started 
March  29,  1923.  Enlargement  was  not  discernible  until  April  29,  when  it 
began  and  continued  at  a  slow  rate  throughout  the  summer.  An  increase 
of  4  mm.  in  diameter  had  been  made  by  September  2,  the  end  of  the 
seasonal  activities. 

No.  4,  the  parent  of  the  older  trunk  of  this  pair,  was  60  cm.  in  diameter 
over  the  bark.  Enlargement  was  coincident  with  that  of  No.  5,  the  smaller 
trunk  coupled  with  it  and  supposedly  arising  from  the  same  base.  The 
features  of  growth  were  approximately  identical  with  those  of  No.  5.  An 
enlargement  of  6  mm.  in  diameter  had  taken  place  by  September  2,  at  which 
time  growth  ceased. 


50 


DENDROGRAPHIC  MEASUREMENTS. 


No.  3  was  one  of  a  small  clump  of  six  trunks  of  nearly  equal  thickness 
arising  around  an  old  stump.  At  the  point  of  attachment  of  the  dendro- 
graph  it  had  a  diameter  of  20  cm.  over  the  bark.  The  soil  was  packed 
about  the  bases  of  the  young  trunks,  which  received  something  more  of 
illumination  than  those  of  Nos.  4  and  5.  Enlargement  was  noticeable  on 
May  1  and  an  increase  of  9  mm.  in  diameter  had  taken  place  by  October  2. 
It  was  noticeable  that  the  daily  variation  in  all  of  these  trees  was  less  than 
that  of  Nos.  1  and  2,  which  were  measured  in  the  previous  season  and  stood 
in  more  exposed  places  where  the  transpiration  might  undergo  wide  fluc¬ 
tuations. 

The  seasonal  period  of  activity  of  No.  1  was  190  days  in  1921,  and  202 
days  in  1922;  that  of  No.  2  in  1922  was  128  days.  The  time  elapsing 
between  beginning  and  end  of  activity  in  1923  wras  153  days  for  No.  3,  the 
smaller  young  trunk  with  some  exposure  to  direct  sunlight,  and  156  days 
for  the  older  trunks  which  stood  on  a  densely  wooded  hillside,  where  the 
direct  rays  do  not  reach  the  ground  or  illumine  anything  except  the  upper¬ 
most  part  of  the  trunks  and  the  crown. 

THE  ARIZONA  WALNUT. 

Nuts  of  Juglans  major,  the  Arizona  walnut,  were  collected  from  trees 
growing  at  the  8,000-foot  level  in  the  Santa  Catalina  Mountains,  near  the 
Desert  Laboratory,  in  the  autumn  of  1908.  These  were  germinated  at  the 


Fig.  6. — Facsimile  of  dendrographic  record  of  trunk  of  Juglans  (lower  part  of  figure) 
and  of  a  nut  of  the  same  tree  in  week  beginning  July  10,  1922.  Noon 
(Nn)  and  midnight  (Mt)  are  marked  on  the  records.  The  vertical  spaces 
are  10  mm.,  the  variations  of  nut  and  trunk  are  amplified  10  times.  The 
coincident  contraction  and  expansion  of  the  two  is  to  be  seen,  the  changes 
being  more  abrupt  in  the  nut  (fig.  7). 


Coastal  Laboratory  in  1909  and  a  few  young  trees  were  preserved  for  com¬ 
parative  experiments  dealing  with  the  activities  of  the  species  in  the  two 
places.  In  1920,  one  tree,  now  11  years  old,  had  attained  a  thickness  of  15 
cm.  at  a  distance  of  80  cm.  above  the  base.  A  dendrograph  was  attached 
at  this  point  on  February  13,  1920,  and  the  tree  kept  under  observation 
during  the  greater  part  of  three  seasons  following.  The  first  year  the  buds 
began  to  unfold  in  the  week  beginning  March  15,  but  no  expansion  of  the 
trunk  showed  until  about  May  3,  when  the  tree  was  in  full  leafage  and  the 


EXPERIMENTAL  INVESTIGATIONS. 


51 


branches  showed  much  elongation.  The  flowers  were  matured  during  the 
week  beginning  May  17.  About  this  time  the  daily  equalizing  variation, 
which  had  not  been  very  marked,  began  to  be  apparent  and  was  very 
noticeable  on  sunny  or  warm  days. 

Enlargement  was  at  an  end  on  August  10,  a  total  increase  of  6  mm.  in 
diameter  having  taken  place.  Some  slight  swelling  was  discernible  after 
this  date,  but  the  resulting  accretion  was  not  more  than  a  small  fraction  of 
a  millimeter.  The  period  in  which  growth  occurred  was  therefore  about 
85  days. 


Fig.  7. — Facsimile  of  dendrographic  records  of  Juglans  in  its  habitat,  Santa  Catalina 
Mountains,  Arizona.  The  varying  rate  of  increase  and  minor  variations, 
in  addition  to  the  daily  changes,  are  illustrated.  (Compare  with  fig.  6.) 

The  vertical  spaces  are  10  mm.  The  variations  in  diameter  are  amplified 
10  times.  The  horizontal  divisions  are  periods  of  6  hours. 

The  instrument  was  taken  down  on  October  7.  It  was  again  attached  on 
April  11,  1921,  and  enlargement  began  on  April  18.  The  flowers  were 
mature  in  the  week  beginning  May  16.  Some  enlargement  continued  until 
September  30,  thus  making  a  period  of  growth  of  165  days,  which  was 
nearly  double  that  of  the  preceding  season,  the  total  increase  being  also 
greater  and  amounting  to  nearly  10  mm.  The  record  was  continued  until 
October  24  (fig.  6). 

The  dendrograph  was  again  attached  to  the  trunk  on  April  6,  1922.  The 
leaves  were  already  unfolding,  but  no  increase  could  be  detected  until 
May  18.  This  continued  until  September  15,  a  period  of  120  days.  The 
total  increase  in  thickness  during  this  time  was  12  mm. 

A  general  correlation  between  the  amplitude  of  variation  in  the  trunk 
and  in  the  nut  was  discernible,  the  greatest  daily  variations  being  in  the 
second  week  in  August,  when  the  nut  had  attained  nearly  mature  size  and 
the  greater  part  of  the  wood  had  been  formed  for  the  season. 


52 


DENDROGRAPHIC  MEASUREMENTS. 


The  variations  from  season  to  season  in  this  tree  are  of  no  little  interest. 
In  being  established  at  this  place,  it  is  put  under  conditions  which  tend 
to  a  much  exaggerated  activity  in  growth.  Such  acceleration  was  attended 
by  wide  variability  from  season  to  season.  The  single  tree  measured  in 
the  habitat  of  the  plant,  as  described  below,  was  a  few  years  older,  but 
made  a  growth  of  only  4  mm.  in  diameter  in  a  seasonal  period  of  95  days. 
The  tree  in  the  coastal  location  showed  growing  periods  of  85,  165,  and  120 
days  in  succeeding  seasons,  with  increases  of  6,  10,  and  12  mm.  in  diameter. 
The  period  of  full  leafage,  in  which  the  formation  of  carbohydrates  in  the 
leaves  might  go  on,  was  probably  double  that  of  trees  in  the  native  habitat, 
and  may  be  held  to  account  for  the  greater  growth,  which  does  not  seem  to 
be  directly  correlated  with  the  duration  of  the  growing-period. 

In  1922,  the  arrangement  was  made  to  record  the  growth  of  one  of  these 
trees  in  the  habitat  from  which  the  nut  was  obtained  that  grew  into  the 
tree,  the  growth  of  which  for  three  seasons  has  been  described  above.  A 
dendrograph  was  attached  to  the  trunk  of  a  tree,  20  cm.  in  diameter, 
growing  on  the  north  slopes  of  the  Santa  Catalina  Mountains  at  an  eleva¬ 
tion  of  7,000  feet.  The  location  was  one  very  favorable  to  the  species,  but 
near  the  upper  limit  of  its  range.  When  the  instrument  was  attached  the 
leaves  were  beginning  to  unfold,  but  the  bast  seemed  dry  and  inactive.  This 
was  on  May  24,  1922.  The  cores  taken  from  the  trunk  were  difficult  to 
interpret,  but  it  may  be  safely  taken  for  granted  that  the  tree  was  between 
15  and  20  years  old,  and  hence  older  than  the  tree  at  the  Coastal  Labora¬ 
tory  which  was  measured  (fig.  7). 

Growth  began  on  June  1,  and  flowers  were  mature  in  mid- July.  The 
record  was  subject  to  various  errors,  but  it  is  estimated  that  a  total  increase 
of  about  4  mm.  in  diameter  was  made  during  the  growing  period  of  95  days. 

GROWTH  OF  NUTS  OF  JUGLANS  MAJOR. 

Some  measurements  of  the  course  of  growth  in  nuts  of  Juglans  calif ornica 
quercina  Babcock  were  made  at  Carmel  in  1918,  which  have  been  previously 
described.1  Among  other  results,  it  was  established  that  these  bodies 
showed  a  retardation  of  growth  after  the  manner  of  the  aerial  members  of 
most  mesophytic  plants.  It  was  also  found  that  the  developing  nuts,  the 
tissues  of  which  are  in  a  highly  hydrated  condition,  receive  water  from 
stems  in  which  there  is  a  decided  “negative”  pressure.  Sections  of  these 
stems  were  seen  to  absorb  as  much  as  25  per  cent  of  their  volume  upon 
being  immersed  in  water.  Sections  of  young  nuts  hydrated  in  water  swelled 
but  1.4  per  cent. 

Similar  measurements  of  a  nut  of  Juglans  major  were  made  at  Carmel, 
beginning  July  3,  1922,  and  continuing  until  full  size  had  been  reached  a 
month  later.  The  nut  had  reached  a  diameter  of  16  mm.  before  it  was 
brought  into  contact  with  the  fused  silica  bearing-rod  of  a  dendrograph 
lever-set,  which  was  arranged  to  give  an  amplification  of  17.  The  age  of 
the  nut  at  the  beginning  of  the  record  was  probably  about  10  days,  or  one- 
fourth  of  its  period  of  enlargement,  with  a  volume  of  about  135  cu.  mm. 
At  the  end  it  had  attained  a  diameter  about  double  that  given  above  and 

1  D.  T.  MacDougal.  Hydration  and  growth.  Carnegie  Inst.  Wash.  Pub.  No.  297.  1920. 

Especially  pp.  162-166. 


EXPERIMENTAL  INVESTIGATIONS. 


53 


had  reached  a  volume  of  1,070  cu.  mm.,  or  about  8  times  the  volume  at  the 
beginning  of  the  experiment.  The  increase  in  diameter  rose  from  0.5  mm. 
daily  at  the  beginning  of  the  first  week  to  0.55  mm.  daily ;  to  0.8  mm.  daily 
during  the  second  week,  then  declined  to  0.65  mm.  daily  during  the  third 
week,  and  to  0.5  mm.  daily  during  the  fourth  week  (fig.  6). 

The  most  marked  feature  of  growth  was  the  cessation  of  enlargement 
early  in  the  forenoon,  followed  by  a  shrinkage,  which  continued  until  mid¬ 
afternoon.  Acceleration  followed,  so  that  by  3  or  4  p.m.  the  diameter  of 
early  morning  was  regained.  The  shrinkage,  or  falling  off  of  the  rate,  was 
less  marked  on  foggy  days. 

Stomata  of  the  leaves  showed  an  enlargement  of  their  openings  beginning 
about  8  a.m. — earlier  on  some  days — which  reached  a  maximum  about 
10  a.m.,  after  which  a  diminution  of  the  aperture  began  which  brought  the 
slits  to  dimensions  equivalent  to  those  of  8  a.m.  The  shrinkage  of  the  nut 
is  therefore  coincident  with  the  period  of  greatest  stomatal  openings  of  the 
leaves.  That  it  also  includes  some  water-loss  from  the  surface  of  the  nut 
is  probable,  but  the  amount  must  be  very  slight.  This  is  indicated  by  the 
fact  that  when  the  nut  was  shaded  on  a  warm  day  the  shrinkage  was  prac¬ 
tically  the  same  as  when  the  nut  was  exposed.  It  would  seem  that  the 
lessened  diameter  of  the  nut  must  be  attributable  to  water  drawn  by  the 
stem  and  leaves  during  the  midday  period.  Bartholomew1  has  shown  that 
such  a  shrinkage  may  take  place  in  lemons,  due  to  withdrawal  of  water 
by  the  transpiring  action  of  the  leaves.  Such  withdrawal  may  result  in  the 
collapse  of  tissues  in  the  lemon.  No  such  effect  was  discernible  in  the 
walnut,  but  this  result  might  be  responsible  for  the  failure  of  development 
of  nuts  in  orchards. 


THE  ARIZONA  ASH. 

The  record  of  the  growth  of  Fraxinus  arizonica  for  two  seasons  at  Tucson, 
Arizona,  has  already  been  described.  (See  Growth  in  trees,  Carnegie  Inst. 
Wash.  Pub.  No.  307,  1921,  pp.  34-36.)  The  dendrograph  was  kept  in  place 
on  this  tree  at  the  close  of  1920  and  throughout  the  season  of  1921.  It  was 
notable  that  the  daily  equalizing  variations  in  the  trunk,  which  are  so 
noticeable  a  feature  of  the  behavior  of  this  tree  during  the  summer  growing- 
season,  had  lessened  with  the  quiescence  of  the  growing  layer  and  with  the 
moist,  cool  weather  of  the  desert  winter.  The  record  for  the  last  few  days 
of  November  and  December  1920,  and  nearly  all  of  January  1921,  was  but 
little  deviation  from  a  straight  line  (fig.  8). 

Some  daily  variation  was  apparent  in  February.  On  February  23  the 
flower-buds  were  enlarging.  This  tree  bore  only  staminate  flowers.  Two 
days  later  enlargement  of  the  trunk  began,  but  the  leaves  did  not  begin  to 
unfold  and  the  branches  to  elongate  until  March  1.  So  far,  this  and  Parkin- 
sonia  aculeata  are  the  only  trees  yet  encountered  which  show  enlargement 
of  the  trunk  before  the  buds  begin  to  show  elongation  of  the  branches. 
Vigorous  growth  continued  until  late  in  August,  when  short  periods  of  a 
few  days  would  occur  when  no  increase  was  noted  from  the  wide  daily 
variations,  alternating  with  other  short  periods  when  some  enlargement 

1  E.  T.  Bartholomew.  II.  Growth-rate,  water-content,  and  acidity  of  lemons  at  different 
stages  of  maturity.  Amer.  Jour,  of  Bot.,  10,  117-126.  1923. 


54 


DENDROGRAPHIC  MEASUREMENTS. 


occurred.  The  last  of  these  terminated  October  6,  which  may  be  taken  to 
be  the  end  of  the  growing-season,  which  included  223  days,  the  longest  yet 
recorded  for  any  tree,  although  it  is  to  be  noted  that  its  activity  was  some- 


Fio.  8. — Arizona  ash  at  Tucson,  Arizona,  with  dendrograph  by  which  a  record  for  two 

years  was  obtained. 


what  fitful  during  5  weeks  of  this  period.  The  total  increase  in  diameter 
during  the  season  amounted  to  19.5  mm.,  which  is  to  be  compared  with  an 
increase  of  26  mm.  in  1919  and  12  mm.  in  1920. 


EXPERIMENTAL  INVESTIGATIONS. 


55 


THE  PALO  VERDE. 

The  palo  verde  ( Parkinsonia  microphylla) ,  of  the  Arizona  and  Sonoran 
deserts,  is  a  small  tree  with  a  smooth  green  skin,  which  branches  near  the 
ground  and  survives  in  places  with  small  water-supply.  Its  growth  is 
extremely  slow.  The  wood  is  soft,  but,  as  shown  by  the  records,  the  woody 
stems  of  this  tree  show  but  little  variation,  which  was  most  marked  in  late 
summer. 

A  dendrograph  was  attached  to  the  base  of  the  trunk  of  a  tree  about 
15  cm.  in  diameter,  in  the  patio  of  the  Desert  Laboratory,  on  January  7, 
1920,  and  was  closely  attended  until  November  1.  No  perceptible  enlarge¬ 
ment  occurred  within  this  time.  This  invariability  seemed  extraordinary, 
in  view  of  the  fact  that  in  the  period  beginning  in  May  the  outer  layers  of 
the  small  trunk  reached  temperatures  over  30°  C.,  and  in  June  40°  and 
41°  C.  were  recorded. 

It  is  evident  that  the  growth  of  this  tree  is  so  slow  that  a  much  higher 
magnification  would  be  necessary  to  follow  its  course. 

The  conditions  under  which  the  measurements  were  made  were  normal 
to  the  habitual  range  of  the  species. 

THE  BAGOTE. 

This  species  ( Parkinsonia  aculeuta)  has  its  northernmost  range  in  the 
vicinity  of  the  Desert  Laboratory,  and  it  is  cultivated  extensively  as  a 
shade  tree  in  Tucson.  It  makes  a  much  taller  trunk  than  P.  microphylla 
and  displays  a  higher  rate  of  growth. 

A  dendrograph,  with  a  floating  frame  of  bario,  was  attached  to  the  trunk 
of  a  tree  about  16  years  old  in  the  grounds  of  the  residence  of  Dr.  H.  W. 
Fenner,  on  February  16,  1921.  The  trunk  had  a  diameter  of  16  cm.,  and 
an  amplification  of  10  was  employed.  The  grounds  were  subject  to  such 
irrigation  as  is  customary  to  keep  grass  and  cultivated  herbaceous  plants 
in  good  condition  in  a  desert  climate. 

Enlargement  began  on  February  27,  before  any  definite  expansion  of  the 
leaves  had  been  made.  It  was  noted  that  these  organs  had  reached  lengths 
of  2  to  5  cm.  on  March  12.  An  increase  of  about  2  mm.  in  diameter  had 
been  made  by  April  5,  when  a  period  of  actual  shrinkage  lasting  6  days 
ensued.  Growth  was  again  resumed,  the  daily  variations  being  very  slight 
and  of  a  character  resembling  those  of  P.  microphylla. 

A  second  period  of  no  growth  came  between  June  12  and  July  2,  in  which 
the  hot,  dry  weather  was  accompanied  by  some  slight  increase  in  the  daily 
variation.  It  is  to  be  noted  that  the  Arizona  ash,  as  described  in  a  separate 
section,  did  not  cease  to  enlarge  during  this  period,  although  it  stood  but  a 
few  yards  away  and  was  furnished  with  the  same  amount  of  water. 

The  growing-period  was  practically  at  an  end  on  October  8,  a  total 
increase  of  10.8  mm.  haying  been  recorded.  The  period  from  the  beginning 
to  the  end  of  the  growing-season  was  193  days,  included  in  which  were 
periods  of  no  action  or  shrinkage  amounting  to  26  days.  It  is  obvious  that 
the  increase  in  diameter  was  near  the  average  for  this  tree. 


56 


DENDROGRAPHIC  MEASUREMENTS. 


THE  SYCAMORE. 

A  dendrograph  of  the  earliest  design  was  attached  to  the  trunk  of  a 
sycamore  tree,  40  cm.  in  diameter,  in  the  Missouri  Botanical  Garden,  during 
the  growing-season  of  1919  by  the  kind  cooperation  of  Dr.  George  T.  Moore 
and  Professor  B.  M.  Duggar.  The  faults  of  the  assembly  were  such,  how¬ 
ever,  that  it  was  deemed  advisable  to  repeat  the  measurements  during  the 
following  year  with  a  lever-set  employing  the  sliding-rod  contact,  using 
material  with  a  lower  temperature  coefficient. 

Such  an  instrument  was  put  in  place  on  March  15,  1920.  Low  tempera¬ 
tures  prevailed  during  the  following  6  weeks,  with  much  precipitation. 
During  this  time  the  pen  traced  a  fairly  direct  line,  there  being  almost  no 
perceptible  daily  variation.  The  buds  began  to  open  in  the  week  beginning 
April  5.  The  first  actual  enlargement  began  on  May  10,  when  the  leaves 
had  not  yet  accomplished  more  than  half  of  their  final  area.  It  is  notable 
that  the  date  was  coincident  with  that  of  beginning  growth  of  the  Populus 
described  in  the  following  paragraph.  Activity  continued  during  the  entire 
summer  and  until  September  12,  the  total  length  of  the  growing-season  thus 
being  125  days.  The  total  increase  in  diameter  is  estimated  to  be  about 
10  mm.  The  recording  pens  failed  to  ink  properly  during  parts  of  several 
weeks,  making  defective  records.  It  is  notable  here,  as  in  the  poplar  mea¬ 
sured  at  this  place,  that  the  daily  variation  was  very  small  and  did  not 
occur  as  abruptly  as  in  the  pines,  for  example. 

THE  CAROLINA  POPLAR. 

A  dendrograph  was  attached  to  a  Populus  deltoidea,  with  a  trunk  35  cm. 
in  diameter,  standing  near  the  laboratory  of  the  Missouri  Botanical  Garden, 
on  December  27,  1919.  The  winter  weather  of  this  region  is,  of  course, 
inclusive  of  rains  and  freezing  weather.  The  record  traced  through  Janu¬ 
ary,  February,  and  early  March  was  irregular  and  broken  and  probably 
included  some  effects  from  ice  formation  on  the  instrument  or  in  the  bark. 
The  measurements  were  under  the  supervision  of  Professor  B.  M.  Duggar, 
to  whom  I  am  indebted  for  many  interesting  notes  concerning  the  behavior 
of  the  tree. 

The  buds  were  observed  to  be  opening  at  the  end  of  March,  at  which 
time  the  surface  and  subsurface  temperatures  were  observed  to  be  ranging 
from  1°  to  23°  C.  Actual  enlargement  was  observable  on  May  10,  at  which 
time  the  leaves  had  not  reached  their  full  expansion,  and  temperatures 
ranged  between  12°  and  26°  C.  The  growing-season  terminated  about 
July  2,  after  an  increase  of  8  mm.  in  diameter  had  been  made.  The  season 
was  thus  seen  to  extend  over  but  53  days.  It  is  to  be  noted  that  the  daily 
variations  were  of  very  restricted  amplitude,  even  in  the  hottest  weather, 
in  which  this  tree  is  in  agreement  with  the  behavior  of  the  other  soft- 
wooded  trunks,  such  as  Parkinsonia  and  P.  macdougalii. 

MacDOUGAL’S  POPLAR. 

The  growth  of  Populus  macdougalii,  which  is  native  to  the  Colorado 
River  Valley  and  of  its  tributaries,  was  carried  on  for  two  seasons.  On 
February  23,  1920,  an  instrument  was  adjusted  to  a  tree  with  a  trunk 


EXPERIMENTAL  INVESTIGATIONS. 


57 


18  cm.  in  diameter  near  the  laboratory  of  the  Agricultural  Products  Com¬ 
pany  at  Continental,  Arizona,  which  was  run  under  the  personal  super¬ 
vision  of  Dr.  W.  B.  MacCallum.  The  floating  frame  was  of  invar  and  the 
recorder  gave  an  amplification  of  4.5,  which  is  too  little  for  a  tree  of  this 
kind.  The  contacts  were  made  by  scraping  away  a  thin  external  layer  of 
the  bark,  exposing  the  green  tissue  underneath. 

The  leaves  had  made  about  one-fourth  of  their  development  and  the 
tree  stood  near  a  ditch  through  which  irrigation  water  flowed  frequently. 
Some  enlargement  was  noticeable  on  April  14,  and  increases  continued  until 
the  end  of  August,  with  a  total  growing-period  of  about  140  days.  During 
this  time  the  trunk  showed  an  increase  of  17  mm.  in  diameter. 

On  February  12,  1921,  a  dendrograph  with  a  floating  frame  of  invar  was 
attached  to  a  tree  near  the  residence  of  Mr.  B.  R.  Bovee  in  Tucson,  and  the 
observations  were  carried  on  by  Mr.  Bovee  during  the  season.  This  tree 
had  been  grown  from  a  cutting  about  3  inches  in  diameter,  and  in  the  10 
years  it  had  been  in  place  had  attained  a  diameter  of  35  cm.  A  core  taken 
with  an  increment  borer  showed  nine  distinguishable  layers  of  wood.  The 
ground  about  the  tree  was  subject  to  irrigation  necessary  to  keep  a  coarse 
lawn  in  condition.  Active  enlargement  began  on  March  5,  at  which  time 
the  fruits  were  full  size  and  about  mature,  but  the  leaves  had  not  attained 
more  than  three-fourths  of  their  full  expansion.  The  flowers  were  noted 
as  opening  on  February  18,  and  the  leaves  as  beginning  to  unfold  a  week 
later,  or  a  few  days  before  growth  began. 

The  end  of  the  period  of  activity  came  on  September  20,  199  days  after 
the  beginning,  with  a  total  enlargement  of  11  mm.  in  diameter.  It  is  to  be 
noted  that  this  period  was  not  one  of  continuous  enlargement.  The  first 
interruption  occurred  early  in  April,  when  a  shrinkage  occurred  from  the 
5th  to  the  11th.  This  followed  a  snowfall  on  the  night  of  the  4th,  with 
temperatures  under  the  bark  of  8°  and  9°  C.,  which  gradually  rose  within 
the  week.  A  similar  period  of  no  growth  was  seen  April  25  to  May  1,  fol¬ 
lowing  3  days  of  high  wind.  Low  temperatures  caused  a  cessation  of 
growth  May  18  to  23.  No  growth  occurred  between  May  27  and  30, 
enlargement  being  resumed  after  irrigation,  suggesting  lack  of  water  as  the 
inhibiting  cause.  The  increase  following  irrigation,  however,  continued  for 
2  days  only,  to  be  followed  by  quiescence  for  5  days.  Irrigation  on  June  6 
had  a  similar  result,  which  was  repeated  with  irrigation  on  the  14th,  20th, 
and  27th.  When  the  summer  rains  began  furnishing  a  more  adequate 
supply  on  July  3  and  4,  the  enlargement  which  resulted  continued  for  a 
full  week,  but  the  week  beginning  July  11  was  one  of  no  growth.  Increase 
following  a  supply  of  water  by  irrigation  or  by  rains  continued  throughout 
the  summer,  it  being  evident  that  the  tree  was  at  all  times  existing  on  a 
marginal  amount. 

It  is  notable  that  the  temperatures  underneath  the  bark  were  at  no  time 
very  high,  31°  C.  being  the  maximum  observation  at  6h30m  p.m.  in  June, 
31°  C.  at  6  p.m.  in  July,  and  28°  C.  in  August.  The  maximum  temperature 
during  March  at  5  p.m.  was  25°  C.,  and  in  April  24°  C.,  while  it  went  no 
higher  than  27°  C.  in  May,  these  three  months  including  the  greater  part 
of  the  enlargement. 


58 


DENDROGRAPHIC  MEASUREMENTS. 


The  daily  variation  was  at  no  time  very  marked,  as  has  been  seen  with 
other  soft-wooded  trunks.  The  interruptions  in  the  growing-season  suggest 
that  the  tree  was  near  the  limit  of  one  of  its  environic  components;  what 
this  might  be  can  not  be  inferred  unless  it  be  an  inadequate  root-system  or 
an  impervious  soil  which  did  not  allow  ready  penetration  by  the  water. 
The  behavior  of  the  trees  of  this  genus  is  of  a  character  suggestive  of  wide 
variations  in  the  water  content  of  the  trunks.  An  interesting  example  of 
this  variation  is  given  by  Professor  Craib,1  who  found  the  water  content  of 
a  trunk  of  Populus  trichocarpa  to  vary  with  the  wind  in  a  singular  manner. 

THE  ARROYO  WILLOW. 

A  dendrograph  was  attached  to  the  trunk  of  a  Salix  lasiolepsis  growing 
on  the  margin  of  a  small  streamway  in  the  garden  of  the  Coastal  Laboratory 
on  January  13,  1922.  The  trunk  was  14  cm.  in  diameter  and  the  tree 
reached  a  height  of  8  meters.  It  was  closely  surrounded  by  a  number  of 
other  trees  of  about  the  same  size,  but  the  crown  was  exposed  to  the  general 
illumination. 

Some  daily  variation  was  observable  even  during  the  moist  weather  of 
the  spring  months,  with  an  ample  supply  of  water  about  the  roots.  No 
enlargement  was  noticeable,  however,  until  May  12,  at  which  time  a  slight 
upward  movement  in  the  course  of  the  recording  pen  could  be  seen.  This 
was  very  gradual  and  ceased  about  August  4.  The  daily  variations  now 
balanced  until  August  27,  when  some  increase  was  again  noticeable,  which 
continued  until  September  8.  The  growing-period,  therefore,  included  a 
total  of  119  days,  with  an  interregnum  of  12  days,  as  noted  above.  The 
increase  in  diameter  amounted  to  1.3  mm. 

MEASUREMENT  OF  YEARLY  INCREASE  IN  CIRCUMFERENCE 
OF  TREE-TRUNKS  BY  MEANS  OF  THE  DENDROMETER. 

A  design  for  a  dendrometer  for  registering  the  total  increase  in  the 
circumference  during  any  period,  especially  that  of  an  entire  growing- 
season,  was  presented  in  previous  publication.  Some  extended  use  has 
been  made  of  a  few  of  these  instruments  during  1921  and  1922.  The  prin¬ 
cipal  feature  of  such  an  apparatus  is  an  encircling  wire  anchored  at  one 
end,  the  other  being  attached,  as  described,  to  a  spindle  turning  freely  on 
its  axis,  thereby  lifting  a  weighted  pointer  upward  along  a  scale  which 
shows  the  increase  in  the  circumference. 

A  complete  belt  of  corrugated-brass  strip  of  30  or  32  gage  is  fastened 
snugly  around  the  tree,  so  arranged  that  the  increase  in  the  tree  will  stretch 
and  straighten  this  belt.  The  inward  folds,  which  carry  triangular  supports 
for  the  encircling  wire,  are  seated  in  the  angles  of  these  folds.  As  the  tree 
increases  these  are  pushed  outward,  carrying  the  encircling  wire  to  a  larger 
circumference,  the  accretion  being  duly  registered  by  the  pointer  on  the 
vertical  scale.  The  selection  of  the  encircling  wire  offered  the  chief  mechan¬ 
ical  problem  in  designing  the  instrument.  As  readings  were  to  be  made 
only  at  long  intervals  and  would  be  of  such  magnitude  as  to  make  tem- 

1  W.  G.  Craib.  Regional  spread  of  moisture  in  the  wood  of  trees.  III.  Notes  from  the 
Roy.  Bot.  Garden,  Edinburgh,  14,  No.  66,  1-8.  1923. 


EXPERIMENTAL  INVESTIGATIONS. 


59 


perature  coefficients  of  but  little  importance,  chief  attention  was  given  to 
getting  a  wire  that  would  be  flexible  enough  to  run  through  the  guide  loops 
and  which  would  not  corrode  by  exposure.  Two  suitable  selections  were 
found.  One  was  the  10-carat  gold  wire  of  the  dentist,  and  the  other  was 
Dr.  Spechtenhauser’s  “wire  silk”  now  used  in  surgery,  being,  in  fact,  fine 
cables  composed  of  several  minute  bronze  wires. 

Two  instruments  of  each  were  attached  to  trunks  of  trees  in  November 
1922.  One  instrument,  with  the  encircling  or  running  wire  of  gold,  was 
belted  about  Monterey  pine  No.  1  at  B,  near  the  dendrograph,  and  in 
October  1922  it  showed  an  increase  of  circumference  during  the  year  of 
4  cm.  The  dendrometer  encircled  the  tree  below  a  whorl  of  branches  and 

the  diameter  measured  by  the  den¬ 
drograph  was  above,  the  two  in¬ 
struments  being  about  30  cm.  apart. 
The  correspondence  between  the 
results  was  quite  as  close,  as  might 
be  expected,  when  a  single  diameter 
and  the  circumference  of  an  irregu¬ 
lar  trunk  are  used  as  a  basis  for 
comparison. 

Another  dendrometer,  with  an 
encircling  bronze  cable,  fastened  to 
the  trunk  of  Quercus  agrifolia 
about  18  cm.  in  diameter,  in  October 
1921,  showed  an  increase  of  3.5  cm. 
in  circumference  in  October  1922, 


Fig. 


9. — Improved  form  of  dendrometer. 
A,  anchorage  and  adjusting-screw 
of  encircling  cable;  B,  spindle  with 
amplifying  disks;  C,  encircling 
cable  of  bronze  or  gold  wire;  D,  D, 
D,  guides  for  encircling  cable;  E, 
corrugated  belt  of  sheet  brass; 
F,  indicator  which  has  moved 
upward  nearly  two  spaces,  showing 
a  similar  increase  in  circumference, 
X;  G,  weight  for  indicator  and  to 
keep  encircling  cable  taut. 


which  would  indicate  an  average  increase  of  1.3  mm.  during  the  intervening 
year.  Such  an  increase  is  in  harmony  with  the  results  of  previous  measure¬ 
ments  by  the  dendrograph. 

One  instrument  was  fastened  around  the  trunk  of  an  oak  of  dimensions 
about  the  same  as  the  one  noted  above,  on  a  seaward  slope,  where  it  was 
exposed  to  fogs  and  winds.  No  more  than  the  most  minute  amount  of 
expansion  could  be  detected  during  the  year.  The  trunk  was  rough  and 
covered  with  lichens,  a  condition  suggestive  of  slow  growth. 

A  fourth  instrument,  fastened  around  the  trunk  of  a  Monterey  pine  in 
the  same  locality  and  subject  to  the  same  exposure,  showed  an  increase  of 
1.3  cm.  during  the  year.  This  indicated  an  increase  of  4  mm.  in  diameter, 
which  is  to  be  compared  with  an  increase  of  1.5  mm.  made  by  Monterey 
pine  No.  12,  which  stood  not  far  distant. 


60 


DENDROGRAPHIC  MEASUREMENTS. 


An  instrument,  with  the  encircling  wire  of  10-carat  gold,  was  attached  to 
Monterey  pine  No.  1  at  A  (fig.  9)  in  January  1923,  at  the  beginning  of  the 
growing-season.  After  the  close  of  growth  in  September  the  indicator  had 
been  raised  42  mm.,  which  was  1.5  times  the  actual  increase  in.  circum¬ 
ference.  The  calculation  of  the  increase  of  the  average  diameter  of  the 
tree  from  these  figures  showed  this  to  be  nearly  9  mm.  The  reduction  of 
the  dendrograph  record  showed  that  the  diameter  measured  by  this  instru¬ 
ment  during  the  period  in  question  was  8.3  mm.  (fig.  9). 

Another  instrument,  with  an  encircling  cable  of  the  wire  silk,  on  a  small 
tree  of  Quercus  agrifolia,  showed  a  movement  on  the  scale  of  70  mm.,  which 
was  1.5  times  the  actual  increase  in  circumference.  This  indicated  an 
increase  of  15  mm.  in  the  average  diameter,  which  is  often  shown  by  young 
trees  of  this  species  in  vigorous  growth. 

THE  SAHUARO. 

The  measurements  of  growth  of  the  cacti  that  have  been  made  at  the 
Desert  Laboratory  show  that  these  plants  undergo  variations  in  volume 
which  are  determined  by  insolation,  water-content  of  the  soil,  and  other 
factors  affecting  transpiration  and  the  water-balance.  Mrs.  E.  S.  Spalding 
found,  as  a  result  of  her  laborious  measurements  of  the  distance  between 
the  apices  of  the  ridges  of  the  trunks  of  Carnegiea  gigantea,  that  the 
trunk  expands  with  accumulated  water  and  shrinks  with  desiccation,  so 
that  at  a  point  2  meters  from  the  base  the  diameter  of  a  sahuaro  was  87 
mm.  greater  at  one  time  in  the  year  than  in  another  in  which  the  conditions 
had  produced  prolonged  desiccation.1  I  have  determined  the  amount  of 
water-loss  that  might  take  place  from  plants  which  were  detached  from 
the  substratum  and  placed  in  a  shaded  room  or  in  the  open  air.  Thus  a 
small  plant  148  cm.  in  length  placed  in  a  shaded  room  lost  8  cm.  in  a  year, 
during  which  time  the  weight  fell  from  32.5  kg.  to  28.7  kg. 

The  general  course  of  the  changes  in  volume  was  followed  by  Mrs. 
Spalding  throughout  several  seasons,  and  it  wTas  seen  that  variations  of 
the  greatest  amplitude  occurred  in  the  median  region  of  the  trunk,  but 
little  change  taking  place  at  the  base,  while  that  at  the  summit  was  less 
than  that  in  the  thickest  or  most  swollen  part  of  the  trunk. 

The  development  of  the  design  of  the  dendrograph  and  other  apparatus 
for  recording  variations  in  volume  of  massive  plants  made  possible  the 
application  of  some  new  methods  of  determination  of  changes  in  volume 
by  which  the  daily  periodicity  could  be  followed  and  a  closer  analysis  made 
of  the  factors  which  cause  such  changes. 

In  the  first  of  such  measurements  the  contact-lever  of  an  auxograph  was 
brought  into  bearing  on  the  bottom  of  the  furrow  at  a  point  15  cm.  from 
the  apex  of  a  Carnegiea  60  cm.  in  height  on  January  4,  1919.  A  firm  sup¬ 
port  was  placed  against  the  opposite  side  of  the  plant,  by  which  arrange¬ 
ment  changes  in  diameter  were  recorded. 

The  general  trend  of  the  record  was  to  show  a  shrinkage  through  all  of 
the  period  until  May  21,  with  slight  temporary  increases  following  a  rain 

1  MacDougal  and  Spalding.  The  water  balance  of  succulent  plants.  Carnegie  Inst.  Wash. 
Pub.  No.  141.  1910. 


Fig.  10.  A — Carnegiea  No.  13,  with  dendrograph  attached.  B,  Detail  of  attachment  of  instru¬ 
ment.  The  bearing  points  are  in  contact  at  bottom  of  the  furrows. 


MWERSITY  OF  ILLINOIS  UBRAftt 


EXPERIMENTAL  INVESTIGATIONS. 


61 


and  favorable  temperatures.  The  daily  equalizing  variations  became  a 
marked  feature  by  May  10.  Increase  of  the  diameter  of  the  stem  began 
about  9  a.m.  and  continued  until  sunset,  when  a  gradual  contraction  ensued, 
which  continued  until  after  sunrise  on  the  following  morning.  A  rainfall 
of  0.75  inch  on  May  22  was  followed  by  enlargement,  which  continued  for 
three  weeks.  The  record  for  the  week  beginning  June  16  was  faulty,  but 
apparently  the  increase  continued  until  June  27,  a  period  of  over  a  month, 
before  shrinkage  again  ensued,  which  continued  until  July  8,  when  the 
summer  rains  began.  The  supply  of  moisture  was  followed  by  increases 
which  continued  until  July  28.  A  few  days  of  shrinkage  and  enlargement 
again  ensued.  The  arrangement  of  the  instrument  was  crude  and  unsatis¬ 
factory,  but  the  records  made  with  it  established  the  fact  that  the  expansion 
and  contraction  sustained  a  relation  to  day  and  night  the  reverse  of  that 
of  woody  trees.  It  was  also  seen  that  in  periods  of  drought  actual  contrac¬ 
tion  which  resulted  in  shortening  of  the  stem  took  place. 

After  some  three  years  of  experience  with  the  dendrograph  on  the  trunks 
of  a  wide  variety  of  trees,  it  was  thought  possible  to  attach  one  of  these 
instruments  to  the  soft  trunk  of  a  tree  cactus.  The  individual  which  had 
been  No.  13  in  the  series  of  plants  under  observation  by  Mrs.  Spalding  was 
selected.  Its  height  as  recorded  by  her  in  1910  was  about  4  meters.  At  the 
close  of  the  observations  recorded  below  in  1923  its  height  was  about  6.5 
meters.  The  dendrograph  was  attached  at  a  point  about  1.2  meters  above 
the  base.  The  contact-screw  of  the  instrument  and  the  bearing-point  of  the 
recording-lever  were  both  put  into  contact  in  the  bottom  of  furrows,  so  that 
the  diameter  or  distance  between  them  was  approximately  40  cm. 

The  trunk  at  this  point  had  a  soft  cortical  layer  several  centimeters  in 
thickness,  a  discontinuous  woody  ring,  and  a  parenchymatous  medulla,  also 
several  centimeters  in  thickness.  It  is  to  be  seen  that  such  a  structure  was 
one  in  which  both  growth  and  fluctuating  variation  could  take  place, 
although  of  lesser  amplitude  than  in  the  upper  parts  of  the  trunk.  The 
supporting  belt  of  wooden  blocks  was  kept  firmly  in  place  at  all  times  by 
the  additional  use  of  a  number  of  wedges  of  soft  wood,  which  were  thrust 
upward  in  the  grooves  of  the  trunk  and  were  adjusted  from  time  to  time. 
This  necessitated  daily  observation,  which  was  done  by  Mr.  B.  R.  Bovee, 
who  also  read  temperatures  from  thermometers  inserted  in  the  trunks  on 
the  eastern  and  western  sides  at  a  level  slightly  above  that  of  the  contact- 
points  of  the  dendrograph  (fig.  10). 

The  instrument  was  set  to  give  an  amplification  of  9,  and  even  at  this  low 
multiplication  the  pen  would  run  off  the  record-sheet  within  a  week,  the 
actual  variation  within  this  period  being  as  much  as  5  cm.  in  some  cases. 

The  measurements  were  begun  on  February  9,  1922.  A  slight  shrinkage 
was  in  progress  which  continued  at  a  varying  rate  until  March  12.  The 
daily  variation  during  this  time  was  very  slight.  The  only  check  in  the 
general  course  of  the  alteration  was  when  three  cloudy  days,  ending  March 
2,  were  followed  by  warm  weather,  so  that  a  small  increase  took  place 
on  three  days.  Shrinkage  was  resumed,  but  a  snowfall  of  4  or  5  inches  on 
the  night  of  March  11  began  to  melt  the  following  afternoon.  No  change 
of  any  amplitude  took  place  until  the  next  day,  when  an  increase  set  in 
which  continued  without  interruption  until  April  12.  Rainfall  had  occurred 


62 


DENDROGRAPHIC  MEASUREMENTS. 


twice  to  increase  the  supply  of  soil  moisture,  and  during  this  month  the 
diameter  of  the  stem  had  increased  34  mm.,  which  thus  balanced  the 
shrinkage  of  8  mm.  which  had  occurred  in  February  and  March  11,  and 
much  beyond.  Shrinkage  of  6  mm.  now  followed  in  the  time  ending 
May  3,  with  very  great  daily  variations.  Three  days  of  swelling  resulted 
in  a  gain  of  1.3  mm. 

A  week  of  shrinkage  showed  a  loss  of  2  mm.;  3  days  of  swelling  a  gain 
of  3  mm.;  28  days  ending  June  26  a  loss  of  14  mm.,  which  was  checked 
twice  but  which  was  not  stopped  until  a  rain  of  0.36  inch  fell.  The  result¬ 
ing  increase  of  2  mm.  was  made  within  a  week,  to  be  followed  by  2  days 
of  equilibrium,  then  a  rapid  shrinkage  of  6  days  in  which  8  mm.  in  thick¬ 
ness  were  lost.  Then  ensued  a  gain  of  2  mm.  in  4  days  and  a  loss  of  7  mm. 
in  7  days,  which  was  terminated  by  rains.  The  combination  of  rains  and 
the  high  temperatures  of  mid-July  caused  a  gain  of  41  mm.  in  the  9  days 
between  July  20  and  29,  and  after  a  check  for  2  days  a  further  swelling  of 
2  mm.  followed.  Beginning  August  2  a  shrinkage  took  place,  ending  August 
25,  which  lessened  the  diameter  9  mm.  Heavy  rains,  amounting  to  1.4 
inches,  caused  an  increase  of  13  mm.  in  3  days,  but  after  this  time  shrinkage 
followed  which  caused  a  loss  of  4  mm.  in  diameter.  Rain  was  followed  by 
a  swelling  of  3  mm.  A  shrinkage  now  set  in  which  continued  from  Sep¬ 
tember  8  until  November  17.  At  the  end  of  this  period  a  total  loss  of  33.6 
mm.  had  taken  place.  A  gain  of  3  mm.  was  registered  in  the  3  following 
days.  Contraction  was  resumed  on  November  20,  which  continued  until 
February  5,  1923,  then,  on  the  anniversary  of  the  beginning  of  the  record, 
some  expansion  began.  In  the  period  from  November  20  to  this  date  a 
further  decrease  in  diameter  of  27  mm.  had  taken  place. 

Features  of  interest  during  this  period  included  a  rain  on  October  28, 
which  was  not  followed  by  any  expansion,  owing  to  the  low  air  tempera¬ 
tures.  No  daily  variations  were  exhibited  on  November  4  and  under  similar 
circumstances,  as  well  as  on  November  13  to  16,  although  the  contraction 
was  checked  following  this  period. 

If,  now,  the  total  expansions  and  contractions  of  the  trunk  as  noted 
above  are  placed  against  each  other,  it  will  be  found  that  the  trunk  had 
undergone  total  contractions  of  118.6  mm.  and  expansions  of  106.3  mm., 
so  that  at  the  end  of  the  first  year  of  measurement  the  trunk  on  the 
measured  radii  had  a  diameter  about  12  mm.  less  than  on  the  same  date  of 
the  previous  year.  The  autumn  and  winter  were  deficient  in  rainfall,  the 
total  being  below  the  average  normal,  and  this  deficiency  continued  during 
the  spring  and  until  midsummer. 

An  expansion  began  on  February  6,  1923,  which  for  a  week  was  charac¬ 
terized  by  small  daily  variations.  The  swelling  being  due  to  rising  tem¬ 
peratures  rather  than  increased  water-supply,  the  accentuated  variations 
soon  were  visible,  however.  After  an  increase  of  4  mm.,  ending  February 
17,  a  decrease  began  which  had  amounted  to  9  mm.  at  its  termination  on 
March  3. 

Rains  and  rising  temperature  now  resulted  in  a  period  of  expansion  by 
which  an  increase  of  30  mm.  was  recorded  by  March  20.  Of  this  amount 
23  mm.  was  gained  in  the  week  beginning  March  5.  Changes  of  such  ampli¬ 
tude  and  speed  made  necessary  daily  adjustments  of  the  instrument.  A 


EXPERIMENTAL  INVESTIGATIONS. 


63 


loss  of  3  mm.  occurred  in  the  period  ending  April  4;  a  gain  of  1  mm.  in  the 
following  week;  a  loss  of  3  mm.  in  the  following  3  days  and  a  gain  of  7  mm. 
in  a  period  of  6  warm  days  terminated  by  a  cold  rain ;  and  a  loss  of  5  mm.  in 
the  10  days  ending  April  29.  The  daily  variations  were  now  becoming  ex¬ 
tremely  accentuated,  and  after  3  days  of  uncertain  action,  expansion  began, 
which  had  increased  the  diameter  by  12  mm.  on  May  11.  A  loss  of  2  mm. 
took  place  in  the  4  days  ending  May  14,  after  which  a  gain  of  5  mm.  took 
place  in  the  5  days  ending  May  19 ;  a  loss  of  1  mm.  ensued  on  the  following 
3  days;  a  gain  of  1.5  mm.  on  the  next  3  days;  a  contraction  beginning 
on  May  25  was  not  checked  until  June  10,  a  decrease  of  10.5  mm.  having 
taken  place.  A  gain  of  2  mm.  was  recorded  in  2  days,  then  on  June  12 
contraction  was  resumed  with  a  loss  of  5  mm.,  which  was  checked  for  2  days 
with  an  indeterminate  gain ;  a  loss  of  2  mm.  ensued  in  the  following  3  days, 
and  a  gain  of  2  mm.  in  the  5  days  ending  June  26.  Then  followed  a  week 
of  slow  loss  with  only  slight  daily  variations,  probably  due  to  cloudiness, 
which  terminated  with  a  rain  on  July  5,  on  which  date  a  rapid  contraction 
took  place.  The  expansion  which  generally  results  from  the  increased  soil- 
moisture  by  rains  did  not  begin  until  July  11,  or  after  the  lapse  of  5  days 
after  the  rainfall.  The  contraction  in  the  previous  15  days  amounted  to 
10  mm.  The  rains  now  came  at  frequent  intervals  and  the  expansion  was 
phenomenal,  amounting  to  42  mm.  in  4  days.  The  rate  fell  off  rapidly  in 
the  fifth  day,  so  that  at  the  end  of  a  further  5  days  the  total  gain  was  but 
7  mm.,  6  days  with  but  little  change  followed,  when  a  loss  of  1  mm.  occurred 
in  6  days,  followed  by  a  gain  of  7  mm.  by  August  19,  when  a  slow  decrease 
set  in  with  gently  varying  daily  changes,  so  that  on  August  25  a  loss  of 
2  mm.  had  been  recorded.  An  increase  of  2  mm.  was  noted  by  August  28, 
after  which  the  variations  for  a  few  days  were  indeterminate.  The  trend 
of  the  variations  was  to  lessen  the  diameter,  however,  so  that  a  loss  of  4 
mm.  had  taken  place  by  September  24.  A  gain  of  2  mm.  had  taken  place 
by  October  1.  If  the  losses  and  gains  for  1923  up  to  this  time  be  plotted 
against  each  other,  an  accretion  of  68  mm.  is  disclosed  over  the  diameter 
of  February  5,  1923,  or  58  mm.  more  than  the  diameter  of  February  1922 
(fig.  11). 1 

Data  obtained  by  Mrs.  Spalding,  wrhich  were  put  into  a  graph  illustrating 
a  paragraph  by  Professor  V.  M.  Spalding2  on  this  subject,  show  that  the 
trunk  of  this  tree  had  a  contraction  from  March  until  near  the  end  of 
June  1906,  and  that  the  expansion  following  the  summer  rains  did  not  bring 
the  trunk  back  to  its  dimensions  in  the  cooler  season.  The  contraction  in 

1  The  dendrograph  record  showed  a  shrinkage  from  October  1  to  2,  1S23,  during  which  period 
a  loss  of  14  mm.  in  diameter  occurred,  the  month  being  rainless.  Rains  beginning  November  2, 
with  a  total  of  2.99  inches  for  the  month,  caused  an  increase  of  17  mm.  during  the  first  half  of 
the  month  'and  a  further  slow  increase  which  continued  with  but  little  interruption  until 
December  31,  1923,  despite  the  low  temperature,  with  an  additional  gain  of  6  mm.  The  ampli¬ 
tude  of  the  daily  variations  during  December  and  also  during  the  greater  part  of  January  1924 
was  small.  The  total  variation  in  January  1924  was  slight,  but  during  the  last  week  in  the 
month  and  in  the  first  week  in  February,  completing  the  two-year  period  of  the  observations,  a 
shrinkage  of  1  mm.  was  recorded.  If  the  net  gain  of  the  previous  three  months  is  added  to  that  of 
October  1,  1923,  it  is  found  that  the  trunk  had  a  diameter  66  mm.  (2.6  inches)  greater  than  at 
the  beginning  of  the  observations,  February  9,  1922. 

2  V.  M.  Spalding.  Distribution  and  movements  of  desert  plants.  Carnegie  Inst.  Wash. 

Pub.  No.  113.  1909.  See  p.  58  and  plate  23. 


64 


DENDROGRAPHIC  MEASUREMENTS. 


the  late  summer  terminated  in  November,  after  which  expansion  began 
which  continued  until  February,  at  which  time  the  circumference  was  prac¬ 
tically  that  of  March  of  the  previous  year. 

It  is  to  be  seen  from  the  foregoing  that  in  Carnegiea  the  fluctuations  in 
volume  due  to  progressive  water-loss  or  accumulation  are  so  great  that 
they  may  completely  mask  permanent  accretions  which  constitute  growth. 
The  decrease  in  diameter  of  a  trunk  may  continue  for  weeks,  or  even 
months,  with  but  little  interruption.  An  increase  due  solely  to  imbibition 
and  accumulation  of  water  may  go  on  for  similarly  extended  periods  in 
such  manner  that  an  observer  who  directed  his  attention  during  such  a 
period  only  might  conclude  that  growth  was  taking  place.  The  variation 
may  affect  the  length  as  well  as  the  diameter  of  the  trunk. 

These  seasonal  variations  in  volume,  being  due  solely  to  the  state  of  the 
water-balance  of  the  trunk,  rest  solely  on  imbibition  and  transpiration,  and 
hence  may  go  on  at  temperatures  and  under  ether  conditions  beyond  the 
limits  at  which  growth  may  take  place. 


Fig.  11. — Facsimile  of  dendrographic  record  of  Carnegiea  for  two  weeks  in  May  1922.  The 
lower  record  shows  continued  contraction  after  a  rain  with  low  temperatures.  The 
upper  illustrates  the  wide  amplitude  of  daily  variations  in  a  period  when  no  growth 
in  diameter  is  taking  place.  Expansion  begins  before  each  noon  day  and  ends  before 
midnight.  The  horizontal  intervals  denote  6  hours  and  the  vertical  spaces  10  mm. 
The  actual  variation  is  amplified  10  times. 

A  rise  of  temperature  without  addition  to  the  soil-moisture  may  cause  a 
swelling,  as  happened  on  3  days  ending  March  2,  1922.  A  similar  increase 
occurred  in  February  1923.  A  rain  on  October  28,  1922,  however,  was  not 
followed  by  an  increase.  The  temperature  at  this  time  being  very  low, 
the  inaction  may  be  ascribed  to  this  factor. 

The  rainfall  at  the  Desert  Laboratory  (table  7)  is  taken  from  a  gage 
within  100  yards  of  the  tree  cactus.  From  the  data  for  1921,  1922,  and 
1923,  given  below,  it  may  be  seen  that  a  decreasing  series  is  formed.  It  is 
also  evident  that  the  soil-moisture  resulting  directly  from  the  rainfall  on 
the  ground  about  the  plant  is  the  leading  factor  in  determining  growth. 

Growth  rests  upon  the  separation  of  young  cells  from  embryonal  elements 
and  their  enlargement,  first  by  accretion  to  the  solid  or  continuous  mass 
of  the  protoplasm,  then  by  distention  in  which  the  osmotic  action  of  the 
organic  substances  dissolved  in  the  vacuolar  solutions  causes  a  ballooning, 


EXPERIMENTAL  INVESTIGATIONS. 


65 


which  greatly  increases  the  volume  of  the  cell  without  adding  to  its  dry 
weight.  Water  is  being  taken  in  by  imbibition  chiefly  during  the  first  stage 
and  by  osmosis  chiefly  in  the  second  stage,  and  is  also  being  lost  by 
evaporation  from  the  external  surface  of  the  cell-masses  at  a  varying  rate 
all  of  the  time.  This  water-loss  is  so  marked,  and  the  balance  of  water  in 
the  cortical  cells  of  the  Carnegiea  is  in  such  a  critical  condition  that  it  is 
impossible  to  fix  upon  the  period  in  which  growth  takes  place.  It  is  gen¬ 
erally  assumed  that  the  enlargement  which  follows  the  increase  of  soil- 
moisture  and  relative  humidity  by  the  summer  rains  includes  growth,  but 
as  all  of  the  increase  which  takes  place  may  be  wiped  out  by  the  contraction 
in  late  summer  and  winter,  this  is  not  established. 


Table  7. — Rainfall  at  Desert  Laboratory ,  Tucson,  Arizona. 


1921 

1922 

1923 

1921 

1922 

1923 

inches. 

inches. 

inches. 

inches. 

inches. 

inches. 

Jan . 

0.25 

0.82 

0.07 

Aug . 

3.20 

1.58 

3.63 

Feb . 

.29 

.16 

.36 

Sept . 

3.44 

1.44 

0.30 

Mar . 

.15 

.94 

.58 

Oct . 

.31 

.  14 

Trace 

Apr . 

.56 

.86 

.39 

Nov . 

.44 

.31 

2.99 

May . 

.00 

1.10 

.02 

Dec . 

.  18 

.  14 

2.24 

65 

£5 

00 

July . 

6.46 

2.19 

2.02 

Total . 

15.93 

10.53 

12.61 

Enlargement  in  the  apical  part  of  a  small  plant  in  the  open  at  the  Desert 
Laboratory  began  in  the  latter  part  of  April  1916,  as  indicated  by  the 
movement  of  spines  upon  which  an  indicator  lever  was  resting.  Another 
plant  had  been  established  in  a  box  of  soil  in  a  glass  house,  and  recording 
levers  of  an  auxograph  put  into  bearing  on  the  tip  of  a  young  spine  and 
upon  the  surface  of  an  areole  near  its  base.  This  was  done  on  April  4. 
Both  spine  and  tissue  were  already  in  a  stage  of  enlargement.  The  plant 
had  been  kept  supplied  with  water,  and  the  chief  alteration  in  the  environ¬ 
ment  consisted  in  the  rise  of  the  temperature  with  the  advance  of  the 
season,  no  artificial  heat  being  supplied. 

Temperatures  were  recorded  by  thermometers  with  the  bulbs  embedded 
in  the  cortex  near  the  bearing-points,  during  growing  periods  of  both  spines 
and  areoles.  When  the  temperature  fell  to  13°  C.  the  areole  ceased  to  grow, 
but  the  spine  was  still  in  a  condition  to  elongate.  The  lowest  temperature 
at  which  the  mass  of  embryonic  cells  was  found  to  enlarge  was  at  15°  C., 
and  this  may  be  taken  to  be  near  the  minimum  with  soil  and  air  conditions 
favorable.  Growth  was  observed  at  40°  C.,  which  is  probably  not  the 
maximum. 

Growth  was  continuous  during  the  month  in  which  these  records  were 
kept,  but  the  influence  of  stomatal  action  wras  as  plainly  apparent  as  in  the 
variations  of  the  diameter  of  the  trunk  as  already  described.  The  shrinkage 
of  the  cells  due  to  excessive  water-loss  while  the  stomatal  slits  were  at  their 
widest  on  some  days  was  greater  than  growth,  so  that  an  actual  contraction 
appeared.  Generally  the  influence  of  the  excessive  transpiration  was  to 
reduce  the  actual  enlargement  to  a  minimum,  so  that  the  recording-pen 
traced  a  line  not  far  from  horizontal.  Acceleration,  which  is  to  be  asso- 


66 


DENDROGRAPHIC  MEASUREMENTS. 


ciated  with  closing  stomatal  slits,  began  between  8  and  10  a.m.,  and 
retardation  was  discernible  by  6  or  8  p.m.,  which  might  in  some  measure 
be  attributable  to  falling  temperatures. 

It  would  appear  as  highly  probable  that  growth  affecting  the  diameter 
of  the  trunks  may  take  place  as  soon  as  the  rise  of  temperatures  in  April 
furnishes  suitable  conditions.  Some  activity  of  the  spines  and  apices  is 
found  at  this  time.  The  flower-buds  also  begin  to  develop  in  May,  and 
come  to  maturity  in  June  during  the  dry  foresummer.  The  high  rate  of 
transpiration  from  the  flowers  may,  in  fact,  affect  the  contraction  of  the 
trunks,  by  reason  of  the  water  which  they  withdraw  from  them. 

While  it  was  possible,  as  noted  above,  to  interpret  the  variations  in  a 
small  plant  in  such  manner  as  to  determine  the  general  relation  of  growth 
to  temperature,  this  could  not  be  done  satisfactorily  with  the  larger  one. 
Thermometers,  with  the  bulbs  thrust  a  few  millimeters  into  the  cortex  on 
the  eastern  and  western  flanks  of  the  trunk  of  the  sahuaro,  above  the  den- 
drograph,  were  installed,  and  these  were  read  early  in  the  morning  and  at 
midday  for  most  of  the  two-year  period  during  which  the  growth  record 
was  kept. 

The  morning  reading  was  made  shortly  after  8  a.m.,  and  as  a  result  of 
the  direct  action  of  the  sun  that  on  the  east  side  was  generally  higher  than 
on  the  west;  a  similar  difference  was  found  at  noon,  although  the  maximum 
on  the  west  side,  as  found  by  other  observations,  might  be  higher.  Tem¬ 
peratures  of  8°  to  21.5°  C.  were  found  during  February  1922,  when  shrink¬ 
age  was  in  progress.  Expansion  followed  a  quickly  melting  snow  on 
March  12,  1922,  and  continued  for  a  month  with  readings  of  6°  to  26.5°  C. 
After  this,  general  action  was  one  of  contraction,  lasting  until  the  summer 
rains  in  July,  with  temperatures  of  the  outer  part  of  the  trunk  as  high  as 
44.5°  C. 

The  notable  expansion  of  mid-July  took  place  after  the  rains,  with 
readings  of  24°  to  40°  C.  Contraction  in  September  took  place  at  24°  to 
36°  C.  After  this  the  temperature  fell  with  the  advance  of  winter,  so  that 
readings  between  4°  and  27°  C.  were  made  in  November,  December,  and 
January.  A  notable  increase  took  place  in  March  at  temperatures  between 
5.5°  and  20.5°  C.  The  temperatures  in  June  wTere  again  higher  than  those 
in  the  rainy  period  in  July.  The  most  marked  gains  of  the  season  were  at 
temperatures  of  25°  to  38°  C. 

It  is  evident  that  in  such  trunks  the  expansion  and  contraction  of  the 
cells  by  varying  water-balance  may  be  such  as  to  mask  the  accretions  due 
to  growth. 

The  daily  equalizing  variations  in  diameter  of  the  trunk  of  the  sahuaro 
constitutes  a  very  striking  feature.  Beginning  at  some  time  in  the  forenoon 
between  8  a.m.  and  noon,  according  to  the  external  conditions  and  the  state 
of  growth,  the  trunk  begins  to  enlarge  and  continues  to  do  so  until  about 
midnight,  when  this  is  checked  and  the  member  passes  into  a  condition  of 
contraction,  which  continues  until  it  is  reversed  on  the  following  forenoon, 
to  be  turned  into  an  expansion.  Such  a  procedure  may  be  followed  day 
after  day,  at  all  times  of  the  year,  the  upward  or  downward  trend  of  the 
line  traced  by  the  recording-pen  being  determined  by  the  resultant  of  the 
agencies  which  affect  the  size  of  the  trunk.  The  principal  factors  con- 


EXPERIMENTAL  INVESTIGATIONS. 


67 


cemed  may  be  taken  to  include  soil-moisture,  as  balanced  against  tran¬ 
spiration.  When  the  trunk  is  receiving  more  water  from  the  soil  than  is 
evaporated  from  its  green  surfaces,  it  will  undoubtedly  increase  in  size  and 


Fig.  12. — Facsimile  of  dendrographic  records  of  Carnegiea  in  1923.  A  period  of 
reduced  daily  variation  in  the  cool  dry  weather  of  January,  one  of  in¬ 
creased  variation  in  March,  and  still  wider  variation  in  April,  are  illus¬ 
trated.  Enlargement  is  seen  in  week  beginning  April  16,  followed  by 
continuous  shrinkage  in  the  dry,  hot  weather  of  May.  The  singular 
variations  of  the  last  week  in  June  were  produced  by  cloudy  and  humid 
weather.  The  abrupt  expansion,  amounting  to  42  mm.  in  diameter, 
during  the  week  beginning  July  9,  was  caused  by  the  absorption  of  soil- 
moisture  from  heavy  rains  falling  on  the  11th.  The  horizontal  intervals 
denote  6  hours,  and  the  vertical  spaces  10  mm.  Actual  variation  is 
amplified  9  times. 

the  heavy  layer  of  very  thin-walled  cortex  forms  a  very  readily  acting 
expansion  mechanism  (fig.  12). 

That  temperature  is  not  a  direct  factor  is  obvious  from  the  fact  that 
although  the  beginning  of  expansion  of  the  trunk  is  coincident  with  high  air 


68 


DENDROGRAPHIC  MEASUREMENTS. 


temperatures,  and  with  a  rising  temperature  of  the  trunk,  this  enlargement 
continues  until  the  temperatures  have  begun  to  fall,  and  for  5  or  6  hours 
more,  in  both  the  air  and  in  the  trunk.  The  period  of  expansion  extending 
from  midday  until  nearly  midnight,  the  direct  action  of  light  may  not  be 
taken  as  a  direct  or  primal  cause  in  the  matter. 

Direct  measurement  of  transpiration  has  not  been  made,  but  it  is  evident 
that  with  a  surface  the  epidermis  of  which  has  a  waxy  outer  wall  the  chief 
water-loss  takes  place  through  the  stomata.  The  action  of  these  organs, 
therefore,  becomes  a  matter  of  prime  interest.  According  to  measurements 
made  for  me  by  Dr.  Gorm  Loftfield,  in  April,  the  stomata  which  are  seen 
to  be  in  a  condition  in  which  the  slits  are  becoming  narrower  are  most  nearly 
closed  about  noon,  and  remain  so  until  about  10  p.m.,  when  they  begin  to 
open.  It  is  probable  that  with  the  advance  of  summer  that  closure  takes 
place  earlier  in  the  day.  It  is  quite  clear,  however,  that  in  any  plant  the 
expansion  phase  of  the  daily  equalizing  variation  of  a  living  member  takes 
place  during  the  period  of  least  water-loss,  and  the  contraction  during  that 
of  the  greatest.  As  may  be  seen  by  reference  to  the  other  sections  of  this 
paper,  the  period  of  closure  of  the  stomata  in  Opuntia  is  between  midfore¬ 
noon  and  evening,  with  corresponding  periods  of  expansion,  while  all  of  the 
woody  trees  upon  which  observations  have  been  carried  out  show  open 
stomata  during  the  daytime,  with  this  period  characterized  by  a  tendency 
more  or  less  expressed  to  show  a  contraction.  Such  a  periodicity  was 
exhibited  by  fleshy  fruits,  legumes,  nuts,  and  stems  of  herbaceous  plants. 

It  is  to  be  noted  that  when  the  trunk  was  in  a  general  condition  by  which 
it  was  getting  larger  continuously,  the  expansion  in  the  daily  variation 
would  be  seen  to  begin  as  much  as  2  hours  before  noon,  while  in  periods  in 
which  a  general  decrease  was  taking  place  the  daily  expansion  would  not 
be  manifest  until  as  late  as  2  p.m.  The  daily  variation  might  be  reduced 
to  zero  during  periods  of  low  temperature,  while  it  reached  the  greatest 
amplitude  in  periods  of  high  temperature  in  the  drier  parts  of  the  year, 
particularly  in  May  and  June,  when  the  air  temperatures  might  reach  40° 
to  45°  C.  At  such  times  the  daily  variation  in  a  diameter  might  be  as  much 
as  2  mm.,  or  one  part  in  200,  which  is  a  much  higher  proportion  than  the 
rate  of  variation  in  any  tree  with  a  woody  trunk. 

GROWTH  OF  OPUNTIA. 

The  general  morphological  features  of  the  flattened  joints  of  Opuntia  and 
the  course  of  their  enlargement,  together  with  many  features  or  variation 
in  length  and  thickness,  have  been  described  in  previous  publications.1 

These  joints  have  the  form  of  flattened  ovoids,  the  course  of  develop¬ 
ment  of  which  may  be  followed  from  a  length  of  2  to  5  cm.  until  maturity 
at  15  to  20  cm.  is  reached  in  the  species  used.  The  joints  are  considered 
to  consist  of  a  number  of  fused  internodes.  The  cambium  remains  active 
throughout  the  entire  member,  although  the  most  active  zone  of  elongation 
soon  assumes  a  median  position  or  nearer  the  apex. 

Several  features  of  the  variation  in  length  and  thickness  could  not  be 
explained  on  the  basis  of  the  facts  previously  obtained,  and  new  series  of 

1  See  especially,  D.  T.  MacDougal.  Hydration  and  growth.  Carnegie  Inst.  Wash.  Pub.  297 
pp.  128-144.  1920. 


♦ 


EXPERIMENTAL  INVESTIGATIONS. 


69 


measurements  were  desirable.  The  course  of  enlargement  of  some  joints 
was  followed  at  Tucson  in  April  and  May  1921,  under  the  condition  in 
which  the  plant  was  found  growing  as  a  native.  Others  were  measured  at 
the  Coastal  Laboratory,  Carmel,  California,  where  the  equable  conditions 
made  possible  an  analysis  of  the  relative  action  of  various  environmental 
factors. 

In  the  earlier  stages  of  growth  the  daily  program  is  not  like  that  of  the 
stems  of  leafy  shoots.  Elongation  was  characterized  by  an  acceleration 
beginning  about  10  a.m.,  which  continued  until  2  p.m.,  when  the  rate 
diminished  for  an  hour  or  two,  then  continued  more  or  less  uniformly  at 
the  lessened  rate  until  the  following  morning. 


Fig.  13. — Auxographic  record  of  joint  Opuntia  at  Tucson  during  entire  period  of  development 
March  23  to  May  23,  1921,  with  rate  of  increase  designated  by  broken  line  below. 
The  baseline  of  the  auxographic  record  was  240  cm.  long.  (Drawing  shows  length 
of  joint  2.)  The  marked  contractions  illustrated  are  not  seen  in  figure  14. 

The  highest  rate  was  coincident  with  the  maximum  temperatures  of  the 
joint  during  the  midday  period;  that  it  is  not  unaffected  by  other  factors 
is  well  proven  by  the  fact  that  the  lessened  rate  begins  while  the  joint  still 
stands  at  a  temperature  very  favorable  to  growth.  The  acceleration  does 
not  ensue,  except  as  initiated  by  rising  temperature,  as  shown  when  young 
joints  having  temperatures  of  9.5°  to  20.5°  C.  for  44  hours,  beginning  on 
the  afternoon  of  April  4,  did  not  display  the  usual  daily  acceleration  on 
the  5th.  On  the  following  day,  when  the  temperature  of  the  joint  rose 
to  28°  C.,  the  usual  acceleration  ensued. 

At  the  end  of  the  initial  or  embryonic  period  of  the  joint  comes  a  juncture 
when  growth  is  not  only  checked  in  mid-afternoon,  but  is  totally  canceled, 
and  the  cancellation  a  few  days  later  is  exaggerated  into  an  actual  shorten¬ 
ing.  The  period  of  retardation  is  at  first  of  about  3  hours’  duration,  ter¬ 
minating  before  6  p.m.  This  is  gradually  extended,  however,  until  shortening 
of  the  joint  does  not  cease  before  10  p.m.  After  this,  elongation  is  resumed 
and  proceeds  at  a  slow  rate  until  mid-afternoon,  when  acceleration  sets  in, 
which  is  slackened  in  mid-afternoon. 


70 


DENDROGEAPHIC  MEASUREMENTS. 


The  next  feature  which  challenges  attention  is  that  of  the  stoppage  of 
growth  noted  above,  which  becomes  accentuated  into  shrinkage,  and  the 
amount  of  this  shrinkage  increases  until  it  equalizes  the  daily  elongation. 
(See  fig.  13  in  illustration  of  these  phases  of  action.)  During  the  last  period 
the  daily  phases  are  not  so  well  defined,  and  elongation  may  begin  earlier 
in  the  day  or  be  deferred,  according  to  the  water-supply  given  the  plant. 

The  known  factors  which  might  influence  the  rate  of  growth  of  Opuntia, 
and  which  are  contributory  to  the  daily  variations,  are  as  follows:  (a)  tem¬ 
perature;  (b)  water-supply  and  transpiration;  (c)  stomatal  action;  ( d ) 
acidity  of  the  sap;  ( e )  stage  of  development. 

The  rational  interpretation  of  the  marked  daily  variations  in  elongation 
of  the  joints  of  Opuntia  may  be  made  only  when  the  bearing  of  all  of  the 
above  factors  or  conditions  are  taken  into  account. 

The  records  of  Opuntia  Nos.  2  and  5  of  the  series  of  1921  have  been 
selected  for  illustration  of  the  action  of  this  plant  at  Tucson  in  the  present 
paper;  Nos.  20  and  21  were  measured  in  the  equable  climate  at  Carmel, 
California. 


Fig.  14. — Auxographic  record  of  Opuntia  grown  at  Carmel  May  21  to  July  25,  1921,  with 
rate  of  elongation  denoted  by  broken  line  below.  The  base-line  of  original  was 
280  cm.  long.  (Drawing  shows  dimensions  X  0.5.)  Daily  reductions  of  growth, 
but  no  contractions  are  seen. 

The  joint  which  developed  in  the  more  equable  climate  at  Carmel,  Cali¬ 
fornia,  showed  some  departures  from  the  above  procedure,  which  is  charac¬ 
teristic  of  plants  in  their  native  habitat.  The  most  noticeable  difference 
is  that  no  actual  shortening  or  shrinkage  of  the  joint  took  place  in  the 
developmental  or  growing  stage. 

No  definite  difference  in  the  duration  of  the  growing-period  was  to  be 
found  in  the  plants  grown  in  the  two  locations.  Two  joints  at  Tucson 
reached  final  lengths  of  115  and  155  mm.  in  50  and  60  days.  Two  joints 
at  Carmel  reached  lengths  of  125  and  130  mm.  in  56  and  60  days. 

The  daily  cycle  included  a  period  of  more  rapid  growth  between  9  a.m. 
and  2  p.m.,  at  temperatures  between  20°  and  37°  C.  during  the  first  40  or 
50  days  of  the  earlier  part  of  the  development  of  the  joint.  This  was  fol¬ 
lowed  by  an  abrupt  change,  in  which  elongation  was  reduced  to  a  low  rate 
at  first  and  later  in  development  to  zero.  Such  retardation  lasted  until  the 
following  morning.  As  the  joint  approached  maturity  the  duration  of  the 
daily  more  rapidly  growing  period  lessened  until  it  was  not  over  2  hours  in 
length.  After  elongation  by  growth  had  come  to  an  end  for  the  season,  a 
type  of  daily  variation,  which  had  been  followed  for  many  months,  as 
described  in  previous  publications,  became  apparent.  By  such  daily  equal¬ 
izing  variations  the  member  was  longest  at  midday,  coming  back  to  mini¬ 
mum  dimensions  early  in  the  next  day. 


EXPERIMENTAL  INVESTIGATIONS. 


71 


If,  now,  all  of  the  results  of  the  measurements  extending  over  many 
years,  and  of  the  transpirational  and  other  studies  made  with  Opuntia,  are 
taken  into  consideration,  the  following  summarized  statement  may  be  made 
as  to  growth  and  daily  variations  in  volume.  The  temperature  at  which 
growth  may  proceed  in  these  plants  includes  a  range  from  9°  to  58°  C.,  the 
maximum  being  the  highest  recorded  for  any  seed  plant.  The  highest  rates 
of  net  elongation  take  place  between  37°  and  49°  C.  in  plants  in  a  habituated 
environment.  These  temperatures  are  taken  from  the  shoots  and  may  be  at 
times  higher  and  lower  than  that  of  the  air.  Operation  at  these  high  tem¬ 
peratures  is  connected  with  a  high  pentosanic  content  of  the  cells,  which  are 
not  so  easily  coagulable,  or  their  state  of  aggregation  altered  by  high  tem¬ 
peratures  as  albuminous  emulsoids. 

The  seasonal  variation  in  unsatisfied  hydration  capacity,  which  may  be 
attributed  chiefly  to  the  relative  changes  in  the  main  components  of  the 
plasmatic  masses  of  the  cells,  are  illustrated  by  the  auxographic  measure¬ 
ments  of  swellings  of  living  sections  and  dried  sheets  of  cells  shown  in 

table  8. 


Table  8. — Seasonal  variation  in  unsatisfied  hydration  capacity  of  Opuntia ,  at  Tucson . 
[Actual  swelling  at  18°  to  18°  C.  in  percentage  of  original  thickness.] 


Date. 

HC1 

0.01N. 

KOH 

0.01N. 

Glycocoli 

0.01M. 

Water. 

Fresh. 

Dried. 

Fresh. 

Dried. 

Fresh. 

Dried. 

Fresh. 

Dried. 

P • 

ct. 

V • 

ct. 

P- 

ct. 

P. 

ct. 

Feb.  12  1919 . 

146 

136 

177 

175 

208 

141 

164 

168 

Dec.  1919 . 

23 

164 

29 

253 

28 

200 

f27l 

130/ 

200 

Jan.  1920 . 

10 

130 

14 

250 

11.3 

175 

13 

140 

Feb.  1920 . 

11 

83 

14.5 

164 

14 

192 

Mar.  1920 . 

7 

300 

10 

380 

6 

310 

9 

310 

Apr.  1920 . 

4.5 

294 

10 

416 

9.4 

370 

7 

388 

May  1920 . 

36 

170 

44 

215 

44 

110 

32 

135 

Feb.  1921 . 

146 

177 

208 

164 

Feb.  1,  1922 . 

26 

140 

26 

130 

33 

200 

Feb.  L  1923.  .  . 

130 

225 

167 

240 

138 

250 

The  swelling  of  living  sections  is  a  resultant  of  the  osmotic  action  of  the 
cell-contents,  alterations  in  permeability  of  wall  and  plasma,  and  the  hydra¬ 
tion  capacity  of  the  jellies  of  the  cell  in  both  wall  and  plasma.  Increase 
in  acidity  by  swelling  living  material  in  HC1  0.01N  was  seen  to  result  in  a 
swelling  less  than  in  KOH  0.01N.  Dried  material  gave  similar  results. 

Later  series  show  that  at  a  concentration  of  HC1  0.001  to  0.0002N  dried 
material  showed  a  hydration  greater  than  in  water,  and  that  this  effect 
continued  past  the  neutral  point  until  a  concentration  of  about  0.01N  KHO 
was  reached.  This  would  indicate  a  protoplasm  in  which  pentosans  and 
soluble  proteins  were  present  in  nearly  equal  quantities.  As  may  be  seen, 
the  swelling  capacity  of  the  dead  material  is  greatest  in  all  the  testing 
solutions  in  March  and  April  in  accordance  with  previous  records,  at  which 
time  the  mucilages  or  pentosans  had  reached  a  high  proportion.  The  course 


72 


DENDROGRAPHIC  MEASUREMENTS. 


of  the  seasons  is  such  that  the  water-deficit,  or  hydration  capacity  of  living 
material,  at  the  end  of  the  winter  dry  season  is  often  relatively  enormous. 
By  reference  to  table  8  and  to  previously  published  data,1  it  is  to  be  seen 
that  sections  of  living  joints  of  Opuntia  swelled  214  per  cent  on  January  3, 
1918;  164  per  cent  on  February  12,  1919,  and  138  per  cent  in  1923.  The 
swelling  for  other  years  since  1918  in  the  corresponding  period  has  been 
13  and  33  per  cent. 

The  relative  action  of  acids  and  water  and  of  three  amino  compounds  is 
illustrated  by  the  results  obtained  at  the  Coastal  Laboratory,  Carmel,  in 
August  1919  (table  9). 


Table  9. — Median  slices  of  living  material  swelled  at  15°  C. 
[Increases  expressed  as  percentages  of  original  thickness.] 


Propionic  acid. 

Alanine. 

Phenyl-alanine. 

Glycocoll. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

0.01M 

6 

8 

12 

12 

0.001 

7.3 

7.5 

6.5 

10 

Water . 

fi  to  8  i).  ct. :  averaee  of  9  sections.  7.3 

Dried  sections: 

0.01 

/  230 

350 

300 

370 

\ 

270 

270 

450 

0.001 

267 

320 

310 

220 

Water . 

250  to  300  p.  ct. 

;  average  of  6  sections,  275. 

I 

These  results  also  illustrate  the  action  of  the  acid  at  0.01N,  and  of  the 
amino  compounds  at  the  same  concentration.  Alanine,  phenyl-alanine,  and 
glycocoll  increase  hydration  beyond  that  possible  in  water  alone  in  con¬ 
firmation  of  results  previously  obtained.  Such  measurements  have  per¬ 
tinent  interest  in  the  analysis  of  the  daily  variations,  especially  with  respect 
to  the  acidity. 

Richards  and  others  have  found  that  the  acidity  of  the  sap  of  growing 
joints  increases  through  the  night  to  a  concentration  where  it  is  equivalent 
to  0.01N  malic  acid  at  daybreak.  Such  a  degree  of  acidity  would  evidently 
tend  to  reduce  the  hydration  capacity  of  the  cell  colloids  and  hence 
lessen  swelling  or  increase  in  size  during  the  period  in  which  the  acids  were 
accumulating. 

There  now  remains  to  be  considered  the  direct  water  relations  as  affecting 
absorption  and  transpiration. 

The  volume  of  the  plant  may  at  any  time  be  affected  by  the  balance 
between  the  intake  at  the  roots  and  loss  by  transpiration.  The  coincidence 
of  the  open  and  closed  conditions  of  stomata  with  phases  of  accelerated  or 
slackened  growth  leaves  but  little  doubt  that  these  organs  are  concerned  in 
an  important  way  with  the  rate  of  water-loss  and  with  consequent  varia¬ 
tions  in  volume.  The  stomata  of  the  Opuntia  used  in  these  experiments 
were  found  by  Dr.  Gorm  Loftfield  to  close  in  mid-forenoon  and  remain  so 
until  mid-afternoon.  Opuntia  versicolor  closes  the  stomata  on  the  surfaces 


1  Hydration  and  growth.  Carnegie  Inst.  Wash.  Pub.  No.  297,  pp.  131,  132.  1920. 


EXPERIMENTAL  INVESTIGATIONS. 


73 


of  its  cylindrical  green  stems  and  does  not  open  them  until  evening.  The 
stomata  of  Carnegiea  gigantea,  the  action  of  which  is  described  in  the  pre¬ 
vious  section,  are  closed  from  about  noon  until  10  p.m. 

If,  now,  the  action  of  these  various  factors  are  correlated,  it  will  be  seen 
that  the  activity  of  a  joint  of  Opuntia  at  any  moment  is  a  resultant  of  the 
complex  agencies  which  may  modify  metabolism,  but  chiefly  hydration  of 
its  colloids. 

Beginning  in  the  morning,  the  decreasing  acidity  of  the  sap  allows  greater 
hydration,  which  is  also  facilitated  by  the  rising  temperature.  Respiration 
and  the  metabolic  processes  would  also  be  speeded  up.  The  closure  of  the 
stomata  in  mid-forenoon  would  lessen  water-loss,  while  the  rate  of  absorp¬ 
tion  was  increasing.  This  conjunction  would  make  for  a  maximum  increase. 

Now,  in  mid-afternoon,  while  all  of  the  above  factors  are  at  an  intensity 
which  makes  for  accelerated  growth,  the  stomata  open  and  the  rate  of 
water-loss  is  so  great  that  enlargement  is  balanced  or  canceled,  and  in  the 
later  stages  of  development  the  loss  is  so  great  as  to  exceed  the  amount  of 
water  which  reaches  the  stem  from  its  source  of  supply.  That  the  deficit 
in  the  stem  is  a  reality  is  accentuated  by  the  fact  that  the  shrinkage  may 
take  place  in  joints  used  as  cuttings,  the  bases  of  which  have  roots  depend¬ 
ing  in  water,  the  joint  having  been  habituated  to  such  a  culture  method. 

Plants  measured  in  the  equable  temperatures  of  Carmel,  and  which  did 
not  reach  the  high  temperatures  of  the  desert,  did  not  show  actual  shrink¬ 
age,  but  the  cessation  or  slackening  of  growth  was  a  daily  occurrence 
coincident  with  stomatal  action.  The  lower  night  temperatures  tended  to 
lessen  transpiration,  but  the  open  stomata  and  the  lessened  hydration 
capacity  of  the  protoplasm,  due  to  accumulating  acidity,  tended  to  increase 
water-loss.  A  slower  rate  of  growth,  therefore,  persists  until  the  closing  of 
the  stomata  on  the  following  day. 

Some  elongation  as  secondary  growth  may  take  place  in  a  joint  of 
Opuntia  in  the  season  following  its  formation.  The  variations  are  of  the 
type  described. 

One  preparation  was  made  by  which  the  growth  in  thickness  of  such  a 
mature  joint  rooted  as  a  cutting  in  sand  was  recorded  by  the  use  of  the 
dendrographic  lever-set.  This  preparation  stood  on  a  bench  near  a  window 
with  a  southern  exposure.  The  record  covered  a  period  of  86  days,  begin¬ 
ning  February  28,  1922.  The  contact-rod  was  arranged  to  make  a  bearing 
on  the  basal  part  of  the  joint,  which  had  a  thickness  of  about  2  cm.  During 
the  first  10  days  of  this  period,  before  the  adventitious  absorbing  roots  had 
been  formed,  the  joint  showed  a  daily  increase  beginning  shortly  before 
10  a.m.,  which  ceased  2  hours  later,  when  shrinkage  ensued,  which  came  to 
equilibrium  in  about  2  hours,  to  be  repeated  on  the  following  day.  Then 
followed  10  days  of  quiescence,  after  which  steady  enlargement  began.  The 
rate  during  the  3  weeks  following  was  very  low,  but  in  April  a  thickening 
began  which  accelerated  to  2  mm.  per  week  during  the  first  week  in  May. 
A  slow  decrease  brought  the  rate  down  to  one-tenth  this  amount  the  last 
week  in  May.  The  daily  increase  during  midday  was  discernible  in  the 
record  on  some  days  only,  and  appeared  to  be  somewhat  belated  in  com¬ 
parison  with  similar  variations  in  length  due  to  similar  causes  on  other 
days.  In  any  case,  the  mechanical  structure  of  the  basal  part  of  the  stem 


74 


DENDROGRAPHIC  MEASUREMENTS. 


would  prevent  any  marked  shrinkage,  such  as  might  occur  on  the  terminal 
half  of  the  joints  in  which  the  fibro-vascular  tissue  is  not  so  heavy  or  so 
firm.  The  total  actual  increase  in  thickness  in  the  joint  measured  was 
about  6  mm.,  the  original  thickness  being  20  mm. 

An  additional  series  of  measurements  of  the  development  of  the  flower- 
bud  was  made.  The  ovary  in  Opuntia  may  be  taken  to  be  sunken  in  a 
short  member  consisting  of  a  modified  stem.  The  chief  feature  of  the 
earlier  stage  of  development  of  the  flower  of  the  Opuntia  studied  consisted 
in  the  enlargement  of  this  cylindrical  ovoid  body  derived  from  the  stem 
which  ultimately  forms  the  bulk  of  the  fruit.  About  the  time  this  has 
reached  full  size  the  sepals  and  petals,  which  are  in  a  small,  compact  cone 
terminal  to  the  ovular  structure,  begin  to  elongate,  so  that  the  auxographic 
record  of  the  elongation  of  the  flower  shows  two  maxima,  one  of  the  ovular 
body  or  fruit,  and  the  other  that  of  the  petals  and  sepals  before  opening. 

Observations  were  made  on  flowers  in  the  habitat  of  the  plant  at  Tucson, 
and  others  in  the  equable  climate  of  the  Coastal  Laboratory,  at  Carmel, 
California.  A  small  flower-bud  4  mm.  in  length  was  brought  under  the 
bearing-arm  of  an  auxograph  at  Tucson  in  May  1922.  Elongation  was  at 
the  rate  of  2  mm.  daily  during  the  first  5  days,  1.4  mm.  daily  during  the 
next  5  days,  3.1  mm.  daily  during  the  next  7  days,  and  2  mm.  daily  during 
the  following  week.  The  development  of  the  petals  now  began,  and  an 
elongation  of  3  to  4  mm.  daily  ensued  until  they  opened  or  separated.  The 
entire  period  of  development  occupied  a  period  of  26  days.  The  tempera¬ 
tures  of  joints  during  this  time  ranged  from  10°  to  51°  C. 

A  similar  bud,  but  slightly  larger,  was  put  under  the  auxograph  at  Carmel, 
June  8, 1922,  and  the  flower  did  not  open  until  41  days  later.  The  tempera¬ 
tures  of  the  joints  were  much  lower,  ranging  from  10°  to  37°  C.  Elongation 
the  first  week  was  at  the  rate  of  1  mm.  daily,  1.2  mm.  daily  during  the 
second  week,  0.6  mm.  daily  in  the  third  week,  and  0.7  mm.  daily  in  the 
fourth  and  fifth  weeks.  The  awakening  petals  now  brought  into  the  record 
new  zones  of  growth,  and  the  rate  now  ran  1  mm.,  2  mm.,  5.5  mm.,  4.5  mm., 
4  mm.,  and  4  mm.  on  the  days  intervening  before  the  opening  of  the  flower. 

A  midday  acceleration  in  both  the  ovular  body  and  in  the  petals  is  to  be 
seen  in  the  record.  Such  a  record  would,  of  course,  also  include  a  similar 
increase  in  the  flat  joint  bearing  the  flower.  It  was  notable  that  the  final 
stages  of  elongation  of  the  petals  was  at  a  much  higher  rate  in  the  flower 
at  the  lower  temperatures  of  Carmel  than  in  the  flower  developing  under 
normal  and  habitual  conditions  at  Tucson,  a  matter  for  which  no  adequate 
explanation  presents  itself. 

VARIATIONS  IN  LEAVES  OF  MESEMBRYANTHEMUM. 

In  some  studies  of  Mesembryanthemum  the  leaves  of  this  succulent  were 
found  to  show  daily  variations  not  parallel  to  those  of  the  joints  of  Opuntia. 
It  has  since  been  found  that  the  Opuntias  differ  among  themselves  as  to  the 
alterations  in  thickness,  relative  water-content,  etc.  These  results,  and 
those  of  other  studies,  show  that  the  behavior  of  various  succulents  does  not 
come  under  any  single  pattern,  and  it  is  seen  that  the  discrepancy  between 
the  action  of  leaves  of  Mesembryanthemum  and  the  joints  of  Opuntia  is 
more  divergent  than  seemed  to  be  the  case  in  previous  experiments. 


EXPERIMENTAL  INVESTIGATIONS. 


75 


Further  tests  were  made  in  the  summer  of  1922  at  Carmel,  where  this 
plant  flourishes  excellently.  The  leaves,  which  are  triangular  in  cross- 
section,  show  faces  which  are  6  to  18  mm.  across.  When  one  face  is  placed 
against  a  support  and  the  bearing-lever  of  an  auxograph  is  placed  against 
the  opposite  angle,  a  thickness  of  about  8  to  10  mm.  of  tissue  is  under 
measurement  in  a  mature  leaf. 

An  illustration  of  the  action  of  this  plant  is  to  be  had  in  the  behavior  of 
a  young  leaf  which  was  arranged  for  measurement  by  a  dendrograph  lever 
on  August  7,  1922.  The  thickness  measured  at  the  beginning  was  about 
5  mm.  According  to  estimations  previously  made,  the  acidity  of  the  sap 
of  these  leaves  is  greatest  in  the  morning  and  decreases  irregularly  through¬ 
out  the  day,  but  not  to  an  extent  which  could  be  taken  as  modifying  seri¬ 
ously  the  hydration  action  of  the  cell  colloids.1  The  stomata,  which  were 
examined  in  connection  with  the  experiments  described  below,  were  closed 
at  sunrise  and  began  to  open  shortly  afterward,  reaching  a  maximum  width 
of  slit  about  midday.  Shortly  afterward  a  diminution  of  the  slit  was 
observable,  and  as  this  was  seen  to  continue  during  the  afternoon,  it  was 
taken  for  granted  that  it  continued  to  nearly  complete  closure  by  daybreak. 

If  the  known  agencies  affecting  the  size  or  growth  of  the  leaf  be  correlated, 
it  will  be  seen  that  the  rising  temperatures  of  the  forenoon  accelerate 
growth,  and  consequently  the  leaf  increases  until  about  noon.  The  higher 
temperatures  also  cause  increased  transpiration,  which  is  coincidently 
accelerated  by  the  widening  stomatal  slits.  A  time  is,  therefore,  reached 
in  the  midday  period  when  water-loss  is  greater  than  the  supply  reaching 
the  leaves,  and  shrinkage  results.  The  high  temperature  continues  to  facili¬ 
tate  transpiration,  but  the  closing  of  the  stomata  which  sets  in  is  accom¬ 
panied  or  followed  by  lessened  shrinkage,  which  gradually  passes  over  into 
an  increase  of  volume,  which  continues  until  the  crisis  made  by  the  con¬ 
junctive  action  of  open  stomata  and  high  temperatures  next  day  at  noon. 

These  phases  of  action  are  clearly  recognizable  in  the  records  of  the 
leaves  of  Mesembryanthemum  in  1922,  which  were  made  by  a  type  of 
apparatus  different  from  that  used  in  making  the  earlier  measurements. 

GROWTH  OF  POTATO  TUBERS. 

Since  the  variations  in  size  or  rate  of  growth  of  aerial  stems  and  of  other 
organs  entails  the  possibility  of  the  loss  of  water  directly  from  their  surfaces, 
in  addition  to  the  draft  that  may  be  made  upon  their  water  content  by 
competing  organs,  it  was  thought  advisable  to  obtain  some  information  of 
the  behavior  of  structures  in  which  the  loss  from  their  own  surfaces  would 
be  negligible. 

The  tubers  of  Solarium  are  short  stems  or  sections  of  stems  in  which  the 
medulla  and  the  cortex  undergo  an  enormous  development  and  the  epidermal 
system  soon  assumes  a  high  protective  value,  and  as  the  tubers  are  embedded 
in  the  soil,  which  is  customarily  very  moist,  the  conditions  offered  are  very 
good  for  testing  this  matter.  I  have  already  pointed  out  that  the  enlarge¬ 
ment  of  tubers  is  checked  or  brought  to  a  standstill  during  the  midday 

1  D.  T.  MacDougal.  Hydration  and  growth.  Carnegie  Inst.  Wash.  Pub.  No.  297.  1920. 

See  pp. 145-152. 


76 


DENDROGRAPHIC  MEASUREMENTS. 


period,  and  that  the  rate  of  growth  of  a  tuber  may  be  accelerated  by  the 
removal  of  competing  tubers. 

The  material  used  was  of  two  varieties,  “Salinas,”  which  is  grown  exten¬ 
sively  in  the  vicinity  of  the  Coastal  Laboratory,  and  “Ashleaf,”  grown  from 
seed  which  was  furnished  by  Suttons  of  Reading,  England.  The  develop¬ 
ment  of  22  tubers  was  recorded  by  the  use  of  the  auxograph  during  1920 
and  1921.  The  behavior  of  Nos.  16  and  21  will  be  discussed  in  detail,  since 
the  records  of  these  two  include  all  of  the  main  features  of  growth,  and  are 
not  exceptional  in  any  way. 

No.  16  was  a  Salinas  and  was  brought  under  measurement  June  3,  1920, 
at  which  time  it  was  10  mm.  in  diameter  and  15  mm.  in  length.  The  auxo- 
graphic  record  showed  a  period  of  enlargement  of  84  days.  Measurements 
were  continued  for  3  weeks  longer.  Allowing  for  the  initial  stage  of  develop¬ 
ment,  the  growth-period  of  the  tuber  may  be  taken  as  about  100  days 
(fig.  15). 


Fig.  15. — The  four  weekly  records  illustrate  course  of  enlargement  daily  and  other  variations  in 
early,  middle,  and  late  stages  of  growth.  The  horizontal  intervals  denote  6  hours,  noon 
(Nn),and  midnight  (Mt)  being  designated.  The  vertical  spaces  are  10  mm.,  and  the 
variations  of  the  tuber  are  amplified  10  times. 

In  all  of  these  experiments  careful  explorations  were  made  of  the  lateral 
underground  branches  of  plants  cultivated  in  large  barrels  of  rich  soil. 
When  a  tuber  suitable  for  measurement  was  found,  a  block  of  wood  or 
cement  was  embedded  in  the  soil  under  the  tuber  to  afford  a  firm  foundation. 
A  support  for  the  auxograph  was  constructed  on  the  rim  of  the  barrel,  which 
had  been  cut  down  to  the  proper  level.  The  vertical  swinging  arm  of  the 
lever,  tipped  with  cork,  was  seated  on  the  upper  surface  of  the  tuber  and 
fine  soil  was  sifted  about  it  to  a  depth  of  2  or  3  cm. 

Analysis  of  the  record,  week  by  week,  of  No.  16  showed  increases  in  the 
vertical  diameter  at  rates  of  0.6  mm.,  0.55  mm.,  0.3  mm.,  0.3  mm.,  0.3  mm., 
0.3  mm.,  0.4  mm.,  0.3  mm.,  0.27  mm.,  0.35  mm.,  0.14  mm.,  0.14  mm.,  and 


EXPERIMENTAL  INVESTIGATIONS. 


77 


0.03  mm.  daily.  At  the  close  of  the  test  the  tuber  had  taken  a  flattened 
cylindrical  shape,  the  diameter  measured  having  increased  from  10  to  27 
mm.,  while  the  horizontal  cross-diameter  reached  34  mm.  The  axial  diam¬ 
eter  increased  during  the  same  time  from  15  mm.  to  57  mm.  As  the  shorter 
diameter  measured  increased  but  2.7  times  its  earlier  dimensions,  and  the 
length  3.8  times,  it  is  evident  that  the  auxographic  record  may  not  be  taken 
as  a  direct  record  of  total  enlargement.  Thus  it  is  highly  probable  that  the 
greatest  extension  in  length  took  place  during  the  third  to  eighth  weeks, 
during  which  time  the  rate  of  increase  of  the  diameter  under  measurement 
was  equable.  The  maximum  of  this  diameter  occurred  at  a  very  early  stage 
of  development,  in  the  first  week  of  measurement,  when  the  tuber  was  not 
more  than  10  days  old  (fig.  16). 


Fig.  16. — Graphs  illustrating  development  of  potato  tuber  No.  16  (see  fig.  15)  from 
June  3  to  September  19,  1921.  The  solid  line,  A,  denotes  the  course  of 
increase  in  size  or  volume,  the  broken  line,  B,  the  rate  of  increase  in  volume^ 
and  the  dotted  line,  C,  the  rate  of  increase  in  diameter  of  the  tuber. 

The  tubers  were  buried  deep  under  a  fine-grained  layer  of  soil,  which 
was  kept  moist,  yet  it  was  seen  that  the  rate  of  increase  slowed  down  during' 
the  daylight  period,  although  the  temperature  was  within  the  favorable 
range.  That  such  slackened  rate  was  not  due  to  a  lower  soil  moisture,  or  to 
increased  transpiration  from  the  surface  of  the  tuber,  was  evidenced  from 
the  fact  that  when  the  soil  was  saturated  by  a  water  drip  during  this  period 
the  rate  was  not  sensibly  increased.  The  slowing  down  of  the  rate  of  growth 
of  a  tuber  in  the  soil  may,  therefore,  be  taken  to  be  directly  connected  with 
the  increase  of  transpiration  from  the  leaves  and  aerial  surfaces,  by  which 
the  supply  available  for  the  tubers  is  lessened. 


78 


DENDROGRAPHIC  MEASUREMENTS. 


On  the  other  hand,  small  tubers  which  developed  on  etiolated  stems  in 
dark  rooms  with  equable  temperature  displayed  a  direct  reaction  to  tran¬ 
spiration.  Enlargement  of  these  structures,  which  have  a  very  thin  epi¬ 
dermal  system,  was  speeded  up  when  they  were  covered  with  filter-paper 
running  to  a  dish  of  water. 

A  somewhat  more  valuable  set  of  records  was  obtained  from  Ashleaf 
No.  21.  This  tuber  was  more  regularly  cylindrical  (8  by  12  mm.)  in  the 
beginning  on  June  24.  On  September  4,  1921,  it  had  reached  dimensions  of 
37  by  41  mm.,  the  increase  in  the  short  diameter  being  almost  wholly  radial. 
It  was  possible  to  treat  the  increments  as  those  of  a  cylinder  occurring 
within  a  period  of  about  65  days.  The  increases  by  transverse  diameter  in 
successive  weeks  were  as  follows:  1.5  mm.,  2  mm.,  2.5  mm.,  1.5  mm.,  1.6 
mm.,  1.3  mm.,  0.8  mm.,  1.2  mm.,  0.4  mm.,  0.6  mm.,  0.3  mm.  The  accretions 
by  volume  were  calculated  as  follows:  1,625  cu.  mm.,  1,628  cu.  mm.,  1,600 
cu.  mm.,  1,738  cu.  mm.,  3,317  cu.  mm.,  1,686  cu.  mm.,  1,870  cu.  mm.,  2,020 
cu.  mm.,  1,296  cu.  mm.,  1,124  cu.  mm.  It  is  thus  to  be  seen  that  while  the 
maximum  rate  of  increase  of  diameter  was  displayed  in  a  very  early  stage 
of  the  tuber  and  in  the  third  week  of  the  observations,  the  maximum  increase 
in  volume  took  place  much  later,  being  in  the  fifth  week.  It  is  also  to  be 
seen  that  in  the  eighth  week,  when  the  increase  in  diameter  was  but  one-half 
that  of  the  maximum,  the  accretion-rate  was  greater  than  during  the 
period  of  maximum  diameter  increase. 

Facts  are  not  available  for  establishing  relations  between  the  total 
carbohydrate  production  and  storage,  but  it  may  be  safely  assumed  that 
the  accretion-rate  represents  a  direct  correlation. 

In  the  earlier  stages  of  development  the  higher  midday  temperatures 
resulted  in  a  marked  increase  in  diameter,  and  this  reaction  was  charac¬ 
teristic  of  over  2  weeks  of  the  observational  period.  This  would  imply  that 
during  the  first  20  or  25  days  of  the  development  of  the  tuber  such  a  reaction 
would  prevail.  After  this,  and  beginning  on  July  6,  a  slight  retardation 
of  growth  ensued,  accompanied  by  positive  shrinkage  in  some  cases.  Pre¬ 
cisely  similar  reactions  are  displayed  by  young  shoots,  which  show  a  very 
marked  shrinkage  on  warm  days  with  high  evaporation.  Such  shrinkages 
take  place  when  the  temperature  of  the  leaves,  as  determined  by  a  thermo¬ 
couple  would  be  20°  and  21°  C.,  and  probably  with  open  stomata.  Dr. 
Loftfield  has  found  a  differential  behavior  of  the  stomata  of  the  upper  and 
lower  surfaces  of  the  leaves,  and  that  they  have  a  tendency  to  remain 
continuously  open,  closing  tardily  under  the  effects  of  a  depletion  of  the 
water  supply,1  a  behavior  which  may  be  held  to  account  for  the  gently 
gradual  daily  variations,  also  seen  in  Populus  and  in  Parkinsonia  aculeata. 

The  variations  in  volume  of  these  tubers,  like  those  of  nuts  of  Juglans, 
and  fruits,  such  as  the  tomato  and  squash,  are  affected  by  the  transpiration 
from  leafy  surfaces  not  directly  connected  with  these  structures. 

THE  GROWTH  OF  THE  SQUASH. 

The  examination  of  the  growth  of  the  tomato  yielded  some  important 
conclusions  as  to  the  variations  in  volume  and  the  physical  basis  of  accre- 


1 G.  Loftfield.  The  behavior  of  stomata.  Carnegie  Inst.  Wash.  Pub.  No.  314.  pp.  27-33.  1921. 


EXPERIMENTAL  INVESTIGATIONS. 


79 


tions.  These  fruits  were  seen  to  be  in  the  category  of  plant  structures  which 
show  a  greater  increase  in  water  than  in  solid  matter  as  they  enlarge  and 
mature. 

Auxographic  records  of  a  fruit  of  the  melon  type  were  undertaken  in 
1920,  to  ascertain  what  parallelisms  might  be  presented  by  these  compara¬ 
tively  large  formations  in  which  a  similar  water  and  solid  matter  relation 
prevails. 

Squash  plants  were  grown  in  good  soil  and  the  vines  were  led  into  a 
sunken  glass  house,  so  that  the  fruits  could  be  supported  on  solid  tables. 
Auxographs  with  simple  levers  were  arranged  to  be  put  in  bearing  on  the 
upper  surfaces,  and  growth  proceeded  in  an  apparently  normal  manner 
(fig.  17). 


Fig.  17. — Auxographs  arranged  to  record  alterations  in  volume  of  squash. 


Squash  No.  1  was  taken  at  a  diameter  of  13  mm.  on  August  7,  1920, 
immediately  after  pollination,  and  record  of  its  variation  in  diameter  was 
kept  until  it  reached  maturity.  The  rate  of  increase  calculated  weekly  was 
at  the  daily  rates  of  1.5  mm.,  3.6  mm.,  2.4  mm.,  2.0  mm.,  0.85  mm.,  and 
0.2  mm.  The  maximum  rate  of  increase  was  displayed  about  the  eleventh 
or  twelfth  day  of  development.  It  will  be  obvious,  however,  that  the  actual 
accretions  are  not  directly  as  those  of  the  diameter  but  are  in  accordance 
with  the  formula  (ttR2)%.  The  total  growth  for  successive  periods  may 
be  visualized  as  shells  on  a  globe  of  ever-increasing  diameter,  and  such  a 
shell  on  a  globe  50  mm.  in  diameter  would  imply  a  far  greater  amount  of 
growth  than  a  similar  thickness  laid  on  a  globe  10  mm.  in  thickness.  The 
greatest  rate  of  increase  in  diameter  was  about  the  eleventh  or  twelfth  day, 
but  the  maximum  accretions  to  the  volume  occurred  on  the  twenty-fourth  to 
twenty-sixth  days,  the  relative  value  of  the  accretions,  week  by  week,  being 
23,  371,  420,  44,  and  240  (fig.  18). 


80 


DENDROGRAPHIC  MEASUREMENTS. 


A  second  fruit,  which  was  14.5  mm.  in  diameter  on  August  9,  1920,  con¬ 
tinued  to  show  some  enlargement  over  a  period  of  nearly  70  days.  The 
daily  rates  of  increase  calculated  weekly  ran  1.5  mm.,  3  mm.,  3.2  mm.,  1.6 
mm.,  0.6  mm.,  0.3  mm.,  0.3  mm.,  0.3  mm.,  0.4  mm.,  0.4  mm.,  and  0.35  mm. 
The  greatest  rate  of  increase  in  diameter  occurred  on  the  eighth  to  tenth 
days  of  observation,  which  began  with  pollination.  The  increments  in 
volume  calculated  weekly  ran  as  follows:  16,  53,  243,  1,176,  482,  210,  180, 
94,  95, 157,  151,  and  103.  The  highest  rate  of  growth  or  actual  accretion  of 
material  took  place  many  days  after  the  highest  rate  in  increase  in  diameter 
was  noted.  The  chief  feature  of  development  of  this  fruit  was  its  long- 
continued  activity  and  revived  growth  in  the  last  20  days  of  its  development. 


A 


B 

C 


Fig. 


18. — Graphs  illustrating  development  of 
squash  No.  1  from  August  7  to  September 
12,  1921.  The  solid  line,  A,  denotes  course 
of  increase  in  size  or  volume,  the  broken 
line;  B,  the  rate  of  accretion  to  volume, 
and  the  dotted  line;  C,  the  rate  of  increase 
in  diameter. 


Dr.  A.  P.  Anderson1  measured  the  growth  of  a  large  pumpkin  in  my 
laboratory  at  the  University  of  Minnesota  in  1898.  He  found  that  the  fruit 
reached  maturity  in  34  days,  and  that  the  greatest  increase  in  weight 
occurred  on  the  eleventh  day  after  pollination.  The  measurements  were 
entirely  by  weight,  being  obtained  by  a  continuously-weighing  apparatus, 
and  hence  may  be  taken  to  be  nearly  identical  with  the  accretions  in  volume 
noted  above.  The  chief  features  of  the  course  of  growth  consisted  in  a 
maximum  rate  at  night,  or  at  a  time  when  transpiration  was  lowest,  and  a 
decrease  during  the  daytime,  when  water-loss  was  greatest.  The  lessened 
rate  during  the  daylight  period  became  a  daily  loss  in  actual  weight  as  the 
fruit  approached  maturity.  Anderson's  results  gave  foundation  for  conclu¬ 
sions  to  the  effect  that  it  was  due  to  transpiration  from  the  surface  of  the 
fruit  and  by  the  depletion  of  the  supply  from  the  stems  by  the  heightened 
evaporation  from  the  leaves. 

1  A.  P.  Anderson.  The  grand  period  of  growth  in  a  fruit  of  Cucurbita  pepo.  Minn.  Bot. 
Stud.,  part  v,  Bull.  No.  9,  238-279.  1898. 


SUMMARY. 


81 


SUMMARY. 

1.  The  observations  on  growth  described  in  the  preceding  pages  were 
made  principally  on  plants  growing  in  the  open  and  under  the  full  influence 
of  their  habitual  environment.  The  experimental  methods  did  not  in  any 
way  modify  the  normal  activity  of  the  plants,  especially  with  respect 
to  trees. 

2.  Continuous  dendrographic  records  of  changes  in  volume  of  various 
species  of  trees  have  been  extended  to  a  total  of  90  seasons,  and  many  of 
the  seasonal  periods  include  the  entire  year. 

3.  In  addition  to  species  the  growth-activities  and  variations  of  which 
have  been  previously  described,  and  to  which  further  contribution  is  made 
in  the  present  paper,  dendrographic  records  of  Carnegiea  gigantea,  Pinu-s 
arizonica,  P.  strobiformis,  Parkinsonia  aculeata,  Salix  lasiolepis,  and 
Sequoia  sempervirens  have  been  made.  The  results  of  extended  studies  of 
the  growth  of  walnuts,  potato  tubers,  and  the  squash  are  also  included. 

4.  The  records  of  the  growth  of  the  Monterey  pine  ( Pinus  radiata) 
comprise  20  years  of  the  above  total,  the  instruments  attached  to  these 
trees  being  operated  throughout  the  year  in  most  cases.  A  continuous 
record  of  one  tree  since  September  1918  by  a  dendrograph  attached  to 
its  basal  section  has  been  made.  A  second  record,  beginning  in  January 
1920,  has  been  made  by  an  instrument  at  8  meters  from  the  base.  A  large 
number  of  trees  have  been  used  for  dissections  and  incidental  experiments. 

5.  The  duration  of  seasonal  growth  is  longest  in  young  trees,  no  limits 
being  observed  in  one  Monterey  pine  in  1922-1923.  Wide  differences  in  this 
matter  are  exhibited  by  older  trees  standing  in  close  proximity.  The  sea¬ 
sonal  period  for  older  trees  at  Carmel  is  from  57  to  225  days. 

6.  The  thickness  of  the  woody  layer  formed  in  any  year  shows  a  general 
correlation  to  the  length  of  the  growing-season,  as  measured  in  any  single 
tree  of  the  Monterey  pine. 

7.  Two  or  more  layers  of  wood  may  be  formed  in  one  year  by  the  Mon¬ 
terey  pine.  So  far  it  has  not  been  possible  to  correlate  the  interrupted 
activity  of  trees  observed  by  the  dendrograph  with  the  formation  of  such 
layers.  Pauses  in  actual  enlargement  may  result  from  the  abrupt  effect 
of  cold  storms  or  short  periods  of  low  relative  humidity. 

8.  The  thickness  of  the  layers  of  wood  formed,  or  the  total  increase  as 
registered  by  the  dendrograph,  shows  no  constant  relation  to  the  total 
amount  of  rainfall  in  the  Monterey  pine.  It  is  suggested  that  the  thickness 
of  a  woody  layer  is  the  resultant  of  the  favorable  conjunction  of  a  number 
of  factors  in  which  seasonal  relative  humidity  may  be  an  important  agency. 

9.  The  tips  of  the  leaders  and  branches,  and  the  tips  of  small  roots, 
begin  to  elongate  before  enlargement  of  the  trunk  is  discernible  in  the 
Monterey  pine.  No  basis  has  been  found  for  the  prevalent  conception  that 
the  activity  which  is  first  visible  in  the  buds  gradually  descends  to  the  trunk 
and  down  the  trunk  to  its  base.  Growth  in  Monterey  pine  No.  1  began 
at  the  base  and  at  a  place  8  meters  above  on  the  same  day  in  five  separate 
years.  Growth  ceased  earlier  at  the  uppermost  place  in  some  years,  but  in 
1923  cessation  occurred  on  the  same  day  in  the  two  places  on  the  trunk. 


82 


DENDROGRAPHIC  MEASUREMENTS. 


The  relation  of  bud  activity  and  the  encircling  sheet  of  cambium  is  discussed 
in  several  trees  in  subsequent  paragraphs. 

10.  The  secondary  thickening  of  a  large  root  of  the  Monterey  pine  began 
some  time  after  the  enlargement  of  the  trunk,  and  continued  for  a  period 
of  only  a  few  weeks  during  the  single  season  during  which  a  record  was 
made. 

11.  Interferences  with  the  conducting  and  transpiratory  systems  were 
made  by  girdling,  topping,  and  defoliation.  The  mechanical  girdling  of  a 
small  tree  near  the  base  by  the  removal  of  the  bark  and  phloem  during  the 
growing-season  checked  enlargement,  but  did  not  materially  alter  the  length 
of  the  season.  Growth  began  in  a  second  season  and  lasted  until  mid¬ 
summer.  No  woody  layer  was  formed  below  the  girdling  zone  following 
the  removal  of  the  girdle.  Food  material,  as  indicated  by  starch,  was 
reduced  in  the  upper  part  of  the  tree  and  was  most  abundant  at  the  end 
in  a  zone  a  meter  or  more  in  width  immediately  above  the  girdle.  Growth 
continued  longer  in  this  region  than  in  any  other  part  of  the  tree.  Mechani¬ 
cal  girdling  of  the  trunk  some  distance  above  the  base  (2  meters)  checked 
enlargement  of  the  trunk  below  temporarily,  but  enlargement  was  resumed 
within  two  weeks.  Killing  a  basal  section  of  a  tree  in  midsummer  by  boiling 
oil  resulted  in  the  cessation  of  growth  within  a  fortnight  and  the  death  and 
desiccation  of  the  tree  within  a  few  weeks. 

12.  The  removal  of  the  upper  part  of  a  tree  with  all  branches  was  followed 
by  the  cessation  of  growth  within  a  fortnight  and  the  death  of  the  tree 
before  the  end  of  the  season.  A  similar  cutting  of  the  trunk  of  another 
tree  which  left  a  few  branches  below  the  cut  resulted  in  retarded  growth, 
but  the  tree  continued  to  live.  Topping  a  young  tree  2  meters  from  the 
base,  leaving  dense  foliage  on  the  many  branches  below,  stopped  growth 
at  once  and  reduced  daily  variations  to  a  minimum.  Some  awakening  of 
dormant  buds  was  seen. 

13.  Defoliation  of  a  young  tree  of  the  Monterey  pine  in  the  middle  of 
the  growing-season  (March)  was  followed  by  a  cessation  of  growth,  and 
a  reduction  of  the  daily  equalizing  variation.  The  young  leaves  failed  to 
attain  normal  size.  Defoliation  in  midsummer,  in  which  the  leaves  nearing 
maturity  were  not  removed,  did  not  materially  alter  the  course  of  growth 
or  of  the  daily  fluctuating  variations. 

14.  The  movement  of  solutions  through  the  stem  of  the  Monterey  pine 
are  found  to  be  slow  when  compared  with  the  rate  in  woody  trunks  with 
large  open  vessels.  The  rate  found  in  June  during  the  growing  season 
was  less  than  that  of  October  at  a  time  when  activity  was  reduced  to  a 
minimum.  The  rate  of  conduction  during  the  night  was  much  less  than 
during  the  daytime,  corresponding  to  the  comparative  transpirational  action 
of  the  leaves  which  show  the  stomatal  slits  opened  wider  in  the  day  than 
at  night.  The  removal  of  the  terminal  of  a  stem  and  its  replacement  by  a 
vacuum-pump  was  found  to  have  a  distinct  effect  on  the  rate  and  distance 
in  the  conduction  of  dyes  upward  in  the  stems  of  the  Monterey  pine.  This 
effect  by  a  vacuum  of  740  mm.  of  mercury  was  exerted  in  stems  as  long 
as  6.5  meters.  No  tests  were  made  with  longer  stems.  Relatively  large 
quantities  of  water  may  be  pulled  through  short  sections  of  the  stem  of  the 
Monterey  pine  by  the  use  of  similar  pressures. 


SUMMARY. 


83 


15.  Practically  all  organs  or  members  tested  with  the  dendrograph  show 
daily  equalizing  variations  in  size  or  volume,  which  are  referable  to  their 
water-balances.  The  condition  of  the  stomatal  slits,  with  implied  effects 
on  the  transpiration-rate,  is  seen  to  be  the  most  important  factor  in  these 
variations.  The  amplitude  of  the  daily  contractions  and  expansions  is 
greatest  in  the  young  stems  of  the  Monterey  pine  and  in  the  upper  or 
younger  parts  of  older  trees.  The  coefficient  of  variation  is  least  in  the 
thickened  roots  of  this  tree.  The  highest  coefficient  is  reached  in  March 
and  April,  at  the  time  when  growth  is  near  the  maximum  rate,  and  it  is 
least  in  October  or  November,  when  activity  is  least.  The  coefficient  of 
expansion  of  a  large  pine  tree  (No.  1)  near  the  base  is  1  part  in  1,250;  of  the 
upper  part,  1  part  in  700.  The  coefficient  of  expansion  of  the  woody 
cylinder  of  a  similar  tree  inside  the  layers  formed  in  the  previous  two  years 
was  1  part  in  2,000,  showing  that  the  fluctuation  was  greatest  in  the  outer¬ 
most  layers,  the  cortex,  and  the  cambium. 

16.  Determination  of  the  coefficient  of  expansion  of  the  floating  frame 
of  a  dendrograph  of  permant,  which  might  constitute  a  correction  in 
measurements  in  the  variation  in  a  tree-trunk,  show  that  this  error  under 
extreme  conditions  is  such  as  would  be  beyond  the  limits  of  experience 
in  measurement  of  trees,  the  maximum  deviation  being  no  more  than  1  part 
in  9,000.  All  of  the  measurements  given  in  the  preceding  paragraphs  were 
made  with  floating  frames  of  invar,  permant,  or  of  fused  silica,  in  which  the 
error  would  be  so  much  reduced  as  not  to  be  measurable  with  any  profitable 
degree  of  exactness. 

17.  The  general  character  of  the  daily  equalizing  variations  is  character¬ 
istic  of  each  species  (fig.  19).  The  suggestion  first  advanced  that  the  ampli¬ 
tude  of  the  daily  variation  would  be  found  to  depend  upon  the  softness 
of  the  wood  and  the  character  of  the  bark  is  not  borne  out  by  the  extended 
results  available.  The  least  variations  are  encountered  in  Populus,  Platanus, 
Salix,  Par  kins  onia,  and  Fagus.  Variations  of  wide  amplitude  are  shown  by 
Fraxinns  and  all  of  the  coniferous  trees.  The  greatest  daily  fluctuations 
are  to  be  seen  in  the  larger  succulents,  such  as  Carnegiea  and  Opuntia. 

18.  The  leaders  and  tips  of  the  branches  of  the  Arizona  pine  ( Pinus 
arizonica)  begin  to  elongate  some  time  before  the  cambium  awakens. 
Enlargement  of  the  trunk  takes  place  with  temperatures  of  13°  to  31°  C. 
of  the  cambium,  and  the  period  of  growth  was  found  to  be  88  to  90  days. 
The  principal  part  of  the  growth  takes  place  following  the  summer  rains. 

19.  The  Mexican  pine  (Pmus  strobijormis)  was  similar  to  the  Arizona 
pine  in  its  growth  habits,  the  seasonal  activity  extending  over  65  days.  The 
tips  of  the  branches  began  to  elongate  before  thickening  of  the  trunk 
was  seen. 

20.  The  thickness  of  the  woody  layers  formed  by  the  Arizona  and 
Mexican  pines  does  not  correspond  directly  to  the  rainfall  of  the  mid¬ 
summer  season  in  which  it  takes  place.  The  precipitation  of  the  previous 
winter  is  followed  by  a  dry  period,  so  that  the  soil  moisture  is  much  reduced 
before  the  temperatures  reach  a  favorable  intensity.  The  woody  layer  of 
1923  in  these  trees  was  very  thick,  and  the  season  was  one  of  continued 
cloudiness  and  high  relative  humidity,  according  to  common  report. 


84 


DENDROGRAPHIC  MEASUREMENTS. 


21.  The  yellow  pine  ( Pinus  scopulorum )  at  7,000  feet,  Flagstaff,  Arizona, 
showed  seasonal  periods  of  growth  of  65  and  72  days  in  two  trees  in  1923. 
The  daily  variation  was  very  marked,  reaching  an  amplitude  of  1  part  in 
350  at  the  time  of  most  rapid  growth.  This  tree  also  stands  in  a  locality 
in  which  the  soil-moisture  resulting  from  the  winter  rains  is  much  reduced 
before  the  temperatures  reach  a  favorable  intensity. 

PINUS  SCOPULORUM 


Fig.  19. — Facsimiles  of  a  weekly  dendrographic  record  of  several  trees  and  of 
Opuntia  to  illustrate  the  variations  in  volume  characteristic  of  these 
plants.  All  are  shown  in  a  state  of  enlargement  by  growth  except  Opuntia. 
The  horizontal  intervals  denote  6  hours,  noon  (Nn)  and  midnight  (Mt) 
being  designated.  The  vertical  spaces  are  10  mm.  on  original  record, 
and  the  variations  are  amplified  10  times,  except  Salix,  which  are  X  16. 


22.  The  redwood  ( Sequoia  sempervirens )  inhabits  the  coastal  drainage 
of  the  middle  and  northern  parts  of  California,  where  some  individuals 
reach  ages  calculated  at  more  than  3,000  years.  Six  seasons  of  measure¬ 
ments  of  growth  are  now  available,  which  were  made  on  five  trees.  Diffi¬ 
culties  in  the  way  of  instrumental  manipulation  has  restricted  the  use  of  the 
dendrograph  to  smaller  trees,  the  largest  of  which  was  probably  not  more 
than  a  century  old.  Equipment  has  been  secured  for  recording  the  varia¬ 
tions  in  trunks  with  a  diameter  of  150  cm.  The  tips  of  some  of  the  branches 
awaken  before  the  cambium.  The  seasonal  activity  of  the  cambium  varies 
from  128  to  202  days.  Pauses  in  enlargement  may  occur  in  short  periods 
of  high  temperature  and  low  relative  humidity. 


SUMMARY. 


85 


23.  The  growth  of  the  trunks  of  the  Arizona  walnut  ( Juglans  major) 
was  measured  in  the  habitat  of  this  species  at  8,000  feet  in  the  Santa 
Catalina  Mountains  in  Arizona  and  at  the  Coastal  Laboratory.  Seasonal 
activity  lasted  over  85  days  in  1920, 165  days  in  1921,  and  120  days  in  1922 
at  the  Coastal  Laboratory.  Growth  continued  for  95  days  in  a  similar  tree 
in  the  Arizona  habitat.  Enlargement  of  the  trunk  did  not  begin  until  the 
young  leaves  were  expanding.  This  occurred  a  month  before  the  maturity 
of  the  flowers  in  the  coastal  location,  and  six  weeks  before  in  the  mountain 
location.  The  daily  variations  of  the  trunk  in  the  habitat  of  the  tree 
were  modified  by  minute  disturbances,  probably  associated  with  cloudiness 
and  storms.  Reduction  of  such  variations  resulted  at  Carmel  by  the  occur¬ 
rence  of  fogs. 

24.  The  development  of  a  nut  of  the  Arizona  walnut  was  followed  at 
Carmel.  Enlargement  was  modified  by  a  contraction  beginning  in  mid¬ 
forenoon  and  lasting  until  mid-afternoon,  coincident  with  the  period  of 
maximum  opening  of  the  stomatal  slits  on  the  leaves.  Contractions  are  to 
be  attributed  to  the  withdrawal  of  water  through  the  stems  by  the  transpir¬ 
ing  action  of  the  leaves. 

25.  Enlargement  of  the  trunk  of  the  Arizona  ash  ( Fraxinus  arizonica) 
begins  within  two  or  three  days  after  the  awakening  of  the  staminate  flowers 
and  about  a  week  before  the  leaves  start.  The  seasonal  activity  of  a  tree 
at  Tucson,  Arizona,  lasted  223  days,  which  is  the  longest  period  recorded 
for  any  tree,  except  that  of  a  young  Monterey  pine  at  the  Coastal  Labora¬ 
tory.  The  daily  equalizing  variations  were  reduced  to  a  minimum  in  the 
winter  season,  and  were  very  marked  during  the  period  of  maximum  growth. 

26.  The  variation  in  the  small  trunk  of  a  palo  verde  ( Parkinsonia  micro - 
phylla)  tree  in  the  patio  of  the  Desert  Laboratory  was  so  small  during  the 
season  of  1920  as  to  be  not  discernible  on  the  dendrograph  record. 

27.  The  bagote  ( Parkinsonia  aculeata)  was  measured  in  1921.  Enlarge¬ 
ment  of  the  trunk  occurred  before  the  leaves  began  to  unfold.  Activity 
extended  over  193  days,  but  several  pauses,  due  to  deficient  water-supply, 
were  included.  This  and  the  Arizona  ash  are  the  only  trees  observed  by 
the  writer  to  show  activity  of  the  cambium  before  the  leaf-buds  awoke. 
It  is  to  be  noted  that  an  enlargement  accompanying  a  rain  was  seen  by 
Dr.  Loftfield  in  Pinus  ponderosa  in  1920  before  the  buds  awoke.1 

28.  The  sycamore  ( Platanus  occidentalis)  measured  in  the  Missouri 
Botanical  Garden  in  1920  had  a  seasonal  activity  of  125  days,  enlargement 
beginning  a  month  after  the  activity  of  the  leaves.  The  daily  variation, 
which  is  never  great,  is  imperceptible  in  the  time  preceding  the  seasonal 
awakening,  and  was  much  like  that  of  Parkinsonia  (fig.  19). 

29.  The  Carolina  poplar  ( Populus  deltoidea)  measured  at  the  Missouri 
Botanical  Garden  in  1920  had  a  seasonal  period  of  but  53  days.  Buds 
awakened  at  the  end  of  March,  but  enlargement  of  the  trunk  was  not 
observable  until  May  10,  at  which  time  the  leaves  had  not  yet  reached 
full  expansion. 

30.  MacDougaPs  poplar  ( Populus  macdougalii)  showed  a  growing-season 
of  124  days  in  a  small  tree  under  irrigation  at  Continental,  Arizona,  in  1920. 


1  D.  T.  MacDougal.  Growth  in  Trees.  Carnegie  Inst.  Wash.  Pub.  No.  307,  p.  29. 


86 


DENDROGRAPHIC  MEASUREMENTS. 


A  larger  tree  near  the  Desert  Laboratory  had  a  seasonal  period  of  199  days 
in  1921,  but  many  interruptions  or  pauses  were  noted.  The  leaves  had 
attained  about  three-fourths  of  their  full  expansion  and  the  fruits  were 
mature  when  enlargement  began.  The  daily  variations  were  very  slight 
in  the  period  of  inactivity,  and  not  very  marked  at  any  time.  This  fact 
has  not  been  correlated  with  conclusions  of  other  authors  that  the  water- 
content  of  the  trunk  may  vary  widely. 

31.  The  arroyo  willow  ( Salix  lasiolepis)  at  the  Coastal  Laboratory  did 
not  begin  growth  until  May  12  in  1922,  at  which  time  the  leaves  were 
mature,  and  showed  a  seasonal  period  of  119  days  with  an  interregnum 
of  12  days.  The  daily  variations  were  of  small  amplitude  at  all  times. 

32.  The  dendrometer  design  has  been  improved  and  materials  found  for 
its  construction,  so  that  it  may  be  placed  on  a  tree  for  periods  of  a  year 
or  more.  The  increase  of  the  circumference  of  the  trunk  may  be  read  from 
a  scale  at  any  time.  Such  instruments  have  been  attached  to  trees  for 
periods  of  two  years. 

33.  A  dendrographic  record  of  the  variations  in  diameter  of  the  trunk 
of  a  sahuaro  (Carnegiea  gigantea)  a  meter  from  its  base  shows  variations, 
due  to  varying  water-balance,  of  such  wide  amplitude  and  long  continuance 
that  it  is  impossible  to  fix  upon  the  time  when  growth,  including  the 
formation  of  new  cells  and  their  enlargement,  began.  It  would  appear 
by  inference  that  the  apex  of  these  massive  stems  begins  to  elongate  in 
April,  before  a  similar  enlargement  takes  place  in  the  main  part  of  the 
trunk.  The  daily  variations  are  approximately  the  reverse  of  those  of 
the  woody  trees  and  of  the  stems  of  most  herbaceous  plants.  Swelling 
begins  in  mid-forenoon  and  continues  until  nearly  midnight,  when  contrac¬ 
tion  sets  in  and  continues  until  the  next  forenoon.  This  is  coincident  with 
the  condition  of  the  stomatal  slits.  These  are  in  a  closing  condition  during 
the  morning  hours  and  are  narrowest  by  noon,  remaining  so  until  nearly 
midnight.  The  amplitude  of  the  variation  may  amount  to  as  much  as  1 
part  in  200  of  the  diameter.  Variations  of  all  kinds  may  be  much  reduced 
by  the  action  of  low  temperatures.  Increase  of  soil-moisture  by  rains 
has  an  effect  by  which  general  enlargement  of  the  trunk  follows  within 
a  day  after  a  rain  in  the  warmer  season.  Such  an  increase  in  diameter, 
amounting  to  42  mm.,  took  place  in  four  days  in  July  1923.  The  general 
relation  of  the  water-balance  of  the  trunk  to  precipitation  and  soil  moisture 
determined  by  Mrs.  E.  S.  Spalding  is  confirmed.  The  diameter  of  a  trunk 
in  the  basal  portion  was  66  mm.  greater  on  February  9,  1924,  than  the 
same  day  two  years  earlier. 

34.  Growth  of  the  succulent  joints  of  Opuntia  has  several  distinctive 
features.  In  the  younger  stage,  enlargement  is  continuous  within  the  tonic 
range  of  temperature,  an  acceleration  being  seen  at  midday.  At  the  end 
of  the  younger  stage  the  records  show  that  an  acceleration  of  enlargement 
begins  in  mid-forenoon  and  continues  until  mid-afternoon,  when  a  retarda¬ 
tion  takes  place  which  is  not  relaxed  in  young  joints  before  6  p.m.  and 
in  the  older  joints  not  until  10  p.m.,  when  elongation  is  resumed  or  accel¬ 
erated.  The  stomatal  slits  are  found  to  be  in  a  narrowed  condition  between 
mid-forenoon  and  mid-afternoon,  which  may  be  taken  to  account  for  the 
increased  enlargement  at  this  time  in  which  the  higher  temperatures  would 


SUMMARY. 


87 


also  have  a  favorable  effect.  The  lessened  hydration  capacity  of  the 
cell  colloids  resulting  from  the  acidity,  which  increases  through  the  night 
to  such  an  extent  that  the  sap  is  equivalent  to  0.01N  malic  acid  at  day¬ 
break,  would  facilitate  water-loss  during  the  night,  with  its  resultant  action 
on  the  enlargement. 

35.  The  proportionate  swelling  of  living  sections  of  Opuntia  in  water 
show  that  at  the  Desert  Laboratory  the  water  deficit  is  greatest  in  February, 
which  may  be  considered  as  a  cumulative  effect  of  the  desiccation  of  the 
previous  autumn  and  of  the  lack  of  absorption  during  the  period  of  low 
temperatures.  The  deficit  decreases  with  rising  temperatures  and  increases 
soil-moisture  until  April.  An  increase  takes  place  in  the  dry  foresummer. 
A  decrease  doubtless  takes  place  during  the  summer  rains,  to  be  followed 
by  an  increase  which  lasts  until  midwinter,  as  noted. 

36.  The  swelling  of  dried  sections  may  be  taken  as  an  index  of  the 
imbibition  capacity  of  the  cell  colloids.  This  feature  in  Opuntia  is  mainly 
determined  by  the  proportion  of  pentosans  or  mucilages  present.  This 
material  is  present  in  greatest  abundance  in  April  and  May,  at  which  time 
its  water-holding  capacity  causes  living  material  to  show  the  least  water 
deficit  and  the  greatest  swelling  when  dried.  The  mixture  of  colloids  in 
the  cell  is  such  that  living  sections  attain  the  greatest  volume  or  turgidity 
in  solutions  in  which  the  pH  ranges  from  3.01  (that  of  HC1  0.001N)  to  11.99 
(that  of  KHO  0.01N) .  It  is  inferred  that  the  pentosans  and  soluble  proteins 
are  present  in  nearly  equal  proportions. 

37.  Joints  of  Opuntia  grown  in  the  equable  climate  at  Carmel  carry  out 
their  entire  development  by  a  daily  behavior  similar  to  that  of  joints  in 
the  younger  stage  in  a  desert  climate.  No  contractions  ensue.  The  water 
deficit  is  low  at  all  times,  as  indicated  by  the  slight  swelling  of  living 
material  when  placed  in  water.  The  swelling  capacity  of  dried  sections 
is  as  great  or  greater  than  that  of  similar  material  matured  in  the  desert 
location,  indicating  a  high  proportion  of  mucilages. 

38.  The  increase  in  thickness  of  the  flattened  joints  of  Opuntia,  which 
may  take  place  in  the  second  and  later  seasons  of  their  existence,  shows 
a  daily  periodicity  not  parallel  in  all  of  its  features  with  those  of  the 
increase  in  length  of  a  young  joint.  The  daily  increase  in  thickness  early 
in  the  season  occurred  only  in  a  short  period  of  about  2  hours,  ending  at 
midday.  With  the  advance  of  the  season  the  increase  showed  only  during 
a  later  period  in  the  day  and  later  than  the  acceleration  in  growth  in  length. 

39.  The  auxographic  record  of  the  development  of  a  flower-bud  shows 
two  maxima,  one  in  which  the  elongation  of  the  ovular  body  or  fruit  is 
elongating  most  rapidly,  and  later  when  activity  in  this  member  is  slowing 
down  the  sepals  and  petals,  which  are  in  a  compact  terminal  cone,  show 
an  acceleration  which  holds  until  they  are  separated  in  the  opening  flower 
and  can  not  be  measured  by  the  auxograph  conveniently.  Flower-buds 
at  Carmel  attained  maturity  in  41  days  at  temperatures  of  10°  to  37°  C., 
and  those  at  the  Desert  Laboratory  opened  in  26  days  at  temperatures 
which  ranged  from  10°  to  51°  C. 

40.  Some  evidence  confirmatory  of  the  earlier  findings,  that  growth  of 
Opuntia  may  go  on  at  temperatures  between  9°  and  58°  C.,  was  obtained. 
The  highest  rates  of  elongation  are  shown  at  temperatures  between  37°  and 
40°  C.  This  is  the  highest  recorded  for  any  seed  plant. 


88 


DENDROGRAPHIC  MEASUREMENTS. 


41.  The  variations  of  the  growing  leaves  of  another  succulent,  Mesem - 
bryanthemum,  offer  some  features  of  interest  in  contrast  with  the  variations 
in  Opuntia.  The  stomatal  slits  begin  to  open  at  sunrise,  reach  a  maximum 
width  at  midday,  then  begin  to  narrow.  Growth  accelerates  with  the  rising 
temperatures  of  the  forenoon  until  the  increasing  transpiration  masks  or 
cancels  growth  and  a  contraction  results.  Transpiration  being  checked 
in  the  afternoon  by  the  narrowing  of  the  stomatal  slits,  enlargement  is 
again  seen,  which,  with  favorable  temperatures,  continues  through  the  night 
and  until  the  opening  stomata  on  the  following  day  again  reduce  the  water- 
balance  and  cause  a  contraction. 

42.  The  development  of  22  potato  tubers  was  recorded  by  auxographic 
apparatus.  These  organs  have  a  period  of  enlargement  which  may  be 
estimated  at  90  to  100  days.  As  they  are  deeply  buried  in  moist  soil, 
the  water-loss  from  their  surfaces  is  slight.  Transpiration  from  the  leaves 
may  reduce  the  supply  within  the  plant  to  such  an  extent  that  a  mid-day 
slackening  of  growth  or  contraction  may  result.  The  maximum  rate  of 
increase  in  volume  is  not  coincident  with  the  highest  rate  of  increase  in 
diameter,  but  generally  follows  a  week  or  two  later.  The  behavior  of 
tubers  is  comparable  to  that  of  nuts  and  fruits. 

43.  Growth  of  the  squash  was  characterized  by  the  widely  prevalent, 
variations  by  which  the  greatest  increase  took  place  at  night,  with  slack¬ 
ened  growth  or  loss  during  the  daylight  period,  when  the  transpiration 
rate  was  highest.  The  features  described  are  in  agreement  with  those 
found  by  Dr.  A.  P.  Anderson  in  1898.  These  fruits  are  included  in  a  type  or 
formations  in  which  the  proportion  of  water  to  the  solid  material  increases 
toward  maturity,  in  contrast  with  members  of  the  shoot  in  which  the  reverse 
relation  prevails.  The  proportion  of  solid  matter  to  water  present  in  joints 
of  Opuntia  may  not  be  readily  ascertained  for  comparison,  but  it  seems 
that  a  similar  increase  in  the  water-content  takes  place  during  the  initial 
and  main  period  of  development  of  these  members.  Increase  in  dry  weight 
ensues  in  the  following  seasons  by  secondary  formations. 


THE  GROWTH  RECORD  IN  TREES. 


BY 

Forrest  Shreve. 


89 


CONTENTS. 


PAGE. 

Introduction .  91 

Monterey  pine  ( Pinus  radiata ) . . . . . . . .  91 

Stump  analyses . 92 

Height  growth  of  saplings .  94 

Seasonal  march  of  growth . 95 

Correlation  of  height  growth  and  diameter  growth .  96 

Diameter  growth  at  different  heights  in  the  trunk .  97 

Double  rings  of  growth . 103 

Redwood  ( Sequoia  sempervirens ) .  104 

Correlation  of  growth  and  rainfall .  106 

Correlation  in  individual  trees .  107 

Correlation  in  groups  of  trees .  Ill 

Correlation  of  growth  and  temperature .  114 

Summary .  115 


90 


THE  GROWTH  RECORD  IN  TREES. 

INTRODUCTION. 

The  annual  formation  of  a  hollow  cone  of  woody  tissue,  enveloping  the 
trunk  and  all  its  ramifications,  is  the  most  important  exponent  of  the  physi¬ 
ological  activity  of  trees.  The  nature  of  wood  formation,  and  the  internal 
and  external  conditions  which  affect  its  character  and  rate,  comprise  a  field 
of  the  greatest  scientific  and  economic  importance.  Much  of  our  knowledge 
of  the  physiology  of  growth  has  been  learned  from  trees,  and  in  many 
respects  they  present  the  most  favorable  material  with  which  to  investigate 
the  many  problems  that  still  require  solution.  Not  only  is  the  tree  an 
organism  with  obvious  practical  advantages  for  the  study  of  the  physiology 
of  growth,  but  it  supplies  equally  favorable  material  for  the  study  of  the 
influence  of  environmental  conditions  on  fluctuations  in  growth-rate  and 
on  geographic  distribution.  In  general,  the  distribution  of  trees  is  much 
more  fully  and  accurately  known  than  that  of  other  plants,  so  that  they 
lend  themselves  to  work  in  which  the  physical  causes  of  distributional 
limitations  are  being  sought.  Furthermore,  the  growth  of  the  trees  of 
temperate  regions  leaves  each  year  a  record  of  the  total  annual  accom¬ 
plishment.  The  ease  with  which  this  record  may  be  read,  and  the  remote 
antiquity  into  which  it  sometimes  extends,  have  recently  given  to  the  tree 
an  added  interest  in  kindred  sciences  as  a  source  of  precise  chronology 
with  respect  to  conditions  known  to  influence  growth. 

The  work  presented  in  the  succeeding  pages  has  been  undertaken  with 
a  view  to  enlarging  our  knowledge  of  the  growth  record  in  trees,  with 
particular  reference  to  the  Monterey  pine  ( Pinus  radiata) ,  and  with  addi¬ 
tional  work  on  the  redwood  {Sequoia  sempervirens) .  Although  a  great 
deal  of  material  is  available  with  reference  to  the  relation  of  age  to  diameter 
for  almost  all  trees  in  the  silva  of  the  United  States,  it  has  seemed  important 
to  amplify  our  knowledge  of  the  growth  record  for  these  two  trees,  on 
which  other  workers  have  also  been  engaged.  It  is  of  great  importance  to 
learn  more  of  the  life-history  of  the  tree,  and  its  comparative  growth  per¬ 
formances  at  different  ages ;  to  keep  in  view  the  fact  that  the  tree  has  three 
dimensions,  and  that  its  growth  record  can  not  be  read  from  a  single  plane 
surface;  and  with  regard  to  growth  influences,  that  these  are  composite, 
and  not  to  be  determined  by  consideration  of  any  one  environmental 
condition. 

MONTEREY  PINE  (Pinus  radiata). 

There  is  probably  no  one  of  our  native  pines  which  has  as  little  commer¬ 
cial  importance  and  at  the  same  time  as  much  interest  to  the  botanist  and 
the  forester  as  the  Monterey  pine.  It  is  found  in  three  localities  on  the 
coast  of  California  and  on  two  of  the  coastal  islands,  these  isolated  occur¬ 
rences  giving  some  ground  to  the  view  that  it  is  an  old  species  formerly 
extending  continuously  over  a  larger  area.  The  most  northerly  locality 
is  between  Ano  Nuevo  Point  and  Santa  Cruz.  The  largest  body  of  forest 
formed  by  this  pine  lies  in  the  Monterey  Peninsula,  and  along  the  coast 
southward  from  there  for  a  distance  of  about  6  miles.  After  a  break  of 

91 


92 


GROWTH  RECORD  IN  TREES. 


nearly  100  miles,  the  tree  again  appears  in  the  vicinity  of  Cambria,  where 
there  were  originally  several  hundred  acres  of  pure  stands,  as  well  as  many 
scattering  trees.  In  the  neighborhood  of  Monterey  it  is  found  from  sea- 
level  to  815  feet,  and  reaches  its  best  development  in  close  proximity  to 
the  sea.  In  the  other  localities  it  is  more  abundant  at  half  a  mile  or  more 
from  the  strand.  In  all  places  it  becomes  very  infrequent  and  local  at 
distances  of  more  than  3  miles  from  the  coast. 

Owing  to  the  limited  occurrence  of  Monterey  pine,  little  has  been  done  in 
studying  its  silvicultural  habits  and  rate  of  growth.  Larsen  has  published1 
some  figures  on  the  relation  of  height  and  diameter,  the  results  of  30  stem 
analyses,  and  a  general  discussion  of  the  characteristics  of  the  tree.  It  has 
long  enjoyed  a  reputation  for  phenomenally  rapid  growth,  based  on  its 
behavior  in  cultivation  and  on  the  observation  of  exceptional  trees  in  its 
natural  range.  In  spite  of  its  restricted  occurrence,  the  Monterey  pine 
is  successfully  cultivated  in  all  but  the  arid  portions  of  California,  as  well 
as  in  the  Eastern  States  and  in  Europe.  In  New  Zealand  and  Australia 
it  has  been  planted  on  a  commercial  scale  with  conspicuous  success. 

During  the  summer  of  1919,  the  writer  made  a  number  of  stump  analyses 
in  recent  cuttings  near  Monterey,  measured  the  height  growth  of  young 
saplings  for  the  growing-season  of  1919,  kept  four  young  trees  under 
observation  and  measured  them  at  several  intervals  from  March  to  October, 
and  made  a  comparison  of  height-growth  and  diameter-growth  in  a  few 
vigorous  young  saplings.  The  data  that  were  secured  are  presented  in 
the  following  paragraphs: 

STUMP  ANALYSES. 

The  stump  measurements  were  made  at  whatever  height  from  the  ground 
cutting  had  taken  place,  usually  about  1  foot,  and  an  allowance  of  one 
year  was  made  in  each  case  for  the  attainment  of  that  height.  The  average 
diameter  was  secured  both  outside  and  inside  bark,  the  total  number  of 
rings  was  counted,  and  on  a  radius  of  average  length  the  increment  of 
radius  was  measured  for  successive  10-year  periods,  beginning  from  the 
center. 


Table  10. — Average  increase  of  diameter  and  area  for  125  trees  of  Pinus  radiata ,  determined 

by  decades  from  center  of  trunk. 


Decade. 

Number 
of  trees. 

Average  increase 
of  diameter. 

Total  area  at 
end  of  decade. 

Increase  in  area 
in  last  decade. 

1 

102 

cm. 

9.6 

in. 

3.8 

sq.  cm. 
75.4 

sq.  in. 
11.8 

sq.  cm. 
75.4 

sq.  in. 
11.8 

2 

102 

12.8 

5.2 

400.9 

62.6 

325.5 

50.8 

3 

64 

10.2 

4.0 

844.7 

132.0 

519.2 

81.1 

4 

37 

8.0 

3.2 

1,306.2 

204.1 

787.0 

122.9 

5 

23 

7.6 

3.0 

1,840.0 

287.5 

1,053.0 

164.5 

6 

5 

6.6 

2.6 

2,358.1 

368.5 

1,305.1 

203.9 

7 

2 

4.8 

2.0 

2,807.2 

438.6 

1,502.1 

234.9 

8 

2 

3.6 

1.4 

3,155.4 

489.2 

1,653.3 

258.3 

1  Louis  T.  Larsen.  Monterey  pine.  Proc.  Soc.  Amer.  Forester.,  vol.  10,  pp.  68-74.  1915. 


YRS 

120 

110 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 


MONTEREY  PINE  (PINUS  RADIATA). 


93 


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CM.:  10  20  30  40  50  60  70  80  90 


.  20. — Graph  showing  relation  of  age  to  diameter  in  Monterey  pine.  Solid  line,  average  for 
125  trees,  broken  line,  average  based  on  decades  of  growth  in  125  trees;  dots  indicate 
trees  growing  on  adobe  soil,  crosses  trees  growing  on  sand. 


94 


GROWTH  RECORD  IN  TREES. 


Analyses  were  made  for  125  trees,  scattered  as  well  as  possible  through 
the  different  size  classes,  and  all  away  from  the  influence  of  streams, 
springs,  or  lakes.  The  stumps  measured  were  in  seven  different  localities, 
from  Asilomar  to  Carmel  Highlands. 

The  results  of  the  stem  analyses  are  given  in  table  10  and  shown  in 
graphic  form  in  figure  20,  for  the  diameters  inside  bark.  The  greatest 
age,  120  years,  was  found  in  an  individual  67  cm.  in  diameter,  while  the 
largest  tree,  84  cm.  in  diameter,  was  101  years  old.  The  most  rapid  growth 
was  found  in  two  trees  aged  51  and  53  years,  which  had  attained  diameters 
of  28  and  31  cm.  respectively,  equal  to  an  average  diameter-growth  of 
about  6  cm.,  or  2.5  inches  per  decade,  which  can  scarcely  be  regarded 
as  a  phenomenal  rate  of  growth. 

In  one  of  the  above-mentioned  trees  it  was  found  that  the  inside  diameter 
at  the  end  of  the  first  decade  was  19.8  cm.  (7.75  in.).  The  five  years  of 
most  rapid  growth  in  this  decade  resulted  in  a  diameter  increase  of  17  cm. 
(6.75  in.).  The  thickest  of  these  five  rings  was  1.8  cm.,  indicating  a 
growth  in  diameter  of  3.6  cm.,  or  nearly  1.5  inches  in  a  single  year.  That 
this  rate  of  growth  is  very  exceptional  appears  obvious  from  the  fact  that 
it  is  6  times  as  great  as  the  average  lifetime  rate  of  the  two  most  rapidly 
growing  trees  in  the  entire  series  of  125  that  were  measured. 

The  solid  line  of  figure  20  indicates  the  average  age-diameter  relation, 
based  on  the  one  inside  bark  measurement  of  each  tree.  The  diameter 
of  each  tree  at  the  end  of  each  decade  of  its  life  was  determined  from  the 
measurements  of  radius,  and  these  diameters  were  averaged  for  the  125 
trees.  The  broken  line  of  figure  20  indicates  the  age-diameter  relation  as 
based  on  the  one  to  seven  measurements  on  each  tree.  Neither  of  these 
graphs  departs  very  far  from  a  straight  line  except  at  the  upper  ends, 
where  both  are  based  on  a  very  small  amount  of  material.  It  appears 
from  these  data  that  the  rate  of  growth  of  the  Monterey  pine  is  maintained 
rather  uniformly  into  its  period  of  advanced  maturity.  If  the  customary 
fall  in  rate  at  advanced  ages  takes  place  in  this  tree,  it  does  so  only  in 
those  extremely  rare  trees  which  survive  more  than  100  years. 

In  the  vicinity  of  Carmel,  3  miles  south  of  Monterey,  the  pine  grows 
on  the  sandy  soil  of  old  stabilized  dunes  and  also  on  a  stiff  adobe.  The 
trees  embraced  in  this  analysis  were  selected  about  equally  in  sites  with 
these  two  types  of  soil,  in  order  to  determine  any  influence  that  this  marked 
difference  might  exert  on  the  rate  of  growth.  In  figure  20  the  crosses 
indicate  the  trees  growing  on  sand  and  the  dots  those  growing  on  adobe. 
It  will  be  seen  that  there  is  only  a  very  slight  indication  of  any  difference 
between  the  rates  of  diameter  growth  in  the  two  groups  of  trees.  This 
is  probably  due  to  the  fact  that  in  the  months  when  the  pines  are  making 
their  greatest  growth  the  two  soils  are  very  similar  with  respect  to  their 
water- content,  although  they  must  always  differ  in  facility  of  aeration  as 
well  as  in  their  mechanical  resistance  to  root  growth. 

HEIGHT  GROWTH  OF  SAPLINGS. 

It  is  generally  true  of  all  pines  that  a  single  whorl  of  lateral  branches 
arises  annually  at  the  summit  of  the  shoot  of  the  preceding  season.  This 
usually  takes  place  in  the  Monterey  pine,  and  furthermore,  a  second,  and 


MONTEREY  PINE  (PINUS  RADIATA). 


95 


even  a  third  whorl  of  lateral  branches  appears  in  the  great  majority  of 
vigorous  saplings,  springing  from  the  shoot  of  that  season,  and  appearing 
at  any  time  from  July  to  September.  The  writer  has  been  informed  by 
Mr.  G.  A.  Pearson  that  this  behavior  is  also  characteristic  of  the  Southern 
long  leaf  pine  ( Pinus  palustris). 

By  reason  of  these  supernumerary  whorls,  it  is  impossible  to  determine 
the  age  of  the  false  internodes  of  the  stem  by  counting  back  from  the  tip 
and  allowing  one  year  for  each  whorl  of  branches,  as  may  be  done  in  other 
pines.  It  is  easy,  however,  to  distinguish  the  growth  of  the  year  from  that 
of  the  preceding  year  by  the  color  of  the  bark,  which  remains  greenish  even 
after  the  appearance  of  a  second  whorl  of  branches  above  it. 

Measurement  of  the  height-growth  of  300  saplings  was  made  in  late 
August  and  early  September.  Owing  to  the  facts  just  related,  it  was  not 
possible  to  do  more  than  measure  the  height-growth  of  the  current  year, 
then  approaching  its  close,  and  the  height  of  the  sapling  at  the  commence¬ 
ment  of  growth  in  the  spring.  In  table  11  are  given  the  results  of  these 


Table  11. — Average  height  (in  centimeters)  of  800  saplings  at  the  end  of  1918  and  average 
growth  in  1919 ,  by  height  classes ,  and  the  percentage  of  the  latter  on  the  basis  of  the  former. 


Height 

of 

group. 

No. 

meas¬ 

ured. 

Average 

height, 

1918. 

Average 

growth, 

1919. 

Per¬ 

centage. 

Height 

of 

group. 

No. 

meas¬ 

ured. 

Average 

height, 

1918. 

Average 

growth, 

1919. 

Per¬ 

centage. 

10  to  19 

27 

15 

13 

86 

90  to  99 

11 

95 

31 

38 

20  29 

34 

25 

19 

76 

100 

109 

9 

104 

25 

24 

30  39 

44 

35 

20 

57 

110 

119 

6 

113 

34 

30 

40  49 

45 

45 

21 

47 

120 

129 

4 

125 

34 

27 

50  59 

46 

54 

24 

44 

130 

139 

3 

131 

32 

24 

60  69 

32 

65 

29 

45 

160 

169 

1 

160 

48 

30 

70  79 

24 

74 

33 

44 

210 

219 

1 

211 

29 

14 

80  89 

11 

85 

30 

35 

measurements,  grouped  in  height  classes  by  increments  of  10  cm.,  on  the 
basis  of  the  height  at  the  commencement  of  the  season.  The  percentage  of 
the  growth  of  the  year  to  all  previous  growth  is  found  to  fall  from  86  per 
cent  in  seedlings  10  to  19  cm.  high  to  24  per  cent  in  saplings  130  to  132  cm. 
in  height.  There  are,  of  course,  many  exceptional  cases  in  which  height  is 
nearly  doubled  in  a  single  year  by  trees  2  to  3  meters  in  height,  particularly 
in  moist  situations  or  in  trees  left  alone  in  clearing. 

SEASONAL  MARCH  OF  GROWTH. 

In  March  1919  measurements  were  made  of  the  length  of  the  main  shoot 
on  several  vigorous  saplings,  which  had  already  made  a  growth  of  32.5  to 
65  cm.  The  same  shoots  were  measured  at  several  intervals  until  the  middle 
of  October,  and  the  results  in  four  cases  are  given  in  table  12.  It  will  be 
seen  that  in  the  case  of  tree  B,  more  than  half  of  the  year’s  height  growth 
had  taken  place  prior  to  March  30,  while  in  trees  E  and  F,  40  per  cent  of 
it  had  taken  place  by  that  date.  The  amount  of  growth  from  August  to 
October  is  very  small  in  all  of  the  cases,  and  this  appears  to  be  true  of  the 
larger  trees  as  well  as  the  saplings.  Although  the  season  favorable  for 
growth  is  exceptionally  long  on  the  California  coast,  the  Monterey  pine 


96 


GROWTH  RECORD  IN  TREES. 


appears  to  have  a  habit  similar  to  that  of  all  other  pines  in  accomplishing 
the  principal  part  of  its  height-growth  in  the  earliest  weeks  of  the  growing- 
season,  although  it  grows  slowly  throughout  at  least  10  months  of  the  year. 


Table  12. — Height  ( data  in  centimeters )  of  main  shoot  formed  in 
1919,  as  measured  at  intervals  during  the  growing-season . 


Mar.  30 

June  12 

July  12 

Aug.  6 

Sept.  3 

Oct.  12 

B 

65.0 

70.0 

77.5 

82.5 

82.5 

C 

32.5 

87.5 

97.5 

102.5 

102.5 

E 

40.0 

82.5 

96.0 

97.5 

97.5 

100.0 

F 

32.5 

72.5 

81.0 

90.0 

97.5 

100.0 

CORRELATION  OF  HEIGHT  GROWTH  AND  DIAMETER  GROWTH. 

For  the  comparison  of  height-growth  with  diameter-growth  a  number  of 
vigorous  saplings  from  4.5  to  6  meters  in  height  were  chosen.  Owing  to  the 


H  D 

100  5 

80  4 

60  3 

40  2 

20  1 

0  0 

■  A 

‘  %  / 

*•  /  #*  *• 

**•  r 

.  \ . 

- 1 - 1  I - 1  1 - 1 

c  \ 

1913  1914  1915  1916  1917  1918  1919 

1916  1917  1918  1919 

1915  1916  1917  1918  1919 

H  D 
160  8 

140  7 

120  6 

100  5 

80  4 

60  3 

40  2 

20  1 

0  0 

D 

E 

/  x  / 

■  / 

-  ’.,T _ 

F 

/  ' 

■  /  V 

1914  1915  1916  1917  1918  1919 

1915  1916  1917  1918  1919 

1915  1916  1917  1918  1919 

Fig.  21. — Graphs  showing  relation  between  growth  in  height  (solid  line), 
in  diameter  at  base  (dotted  line) ,  and  diameter  halfway  between 
base  and  top  (broken  line)  for  6  young  trees  of  Monterey  pine. 

previously  mentioned  appearance  of  more  than  one  whorl  of  branches  per 
annum,  it  was  necessary  to  cut  across  each  of  the  false  internodes  and  count 
the  rings  in  order  to  determine  the  number  of  internodes  involved  in  the 
height-growth  of  each  year.  The  growth  in  diameter  was  measured  on  the 
stumps  about  10  cm.  from  the  ground,  and  also,  in  a  few  cases,  at  one  of  the 
cross-sections  midway  between  the  top  and  base  of  the  trunk. 

The  comparison  of  height-growth  with  diameter-growth  for  six  represen¬ 
tative  individuals  is  shown  graphically  in  figure  21.  It  might  be  presumed 


MONTEREY  PINE  (PINUS  RADIATA). 


97 


on  a  priori  grounds  that  there  would  be  (1)  a  positive  correlation  between 
the  two  phases  of  growth,  due  to  an  identity  between  the  conditions  favor¬ 
ing  each  of  them;  (2)  a  negative  correlation,  due  to  the  diversion  of  mate¬ 
rials  to  the  one  phase  of  growth  at  the  expense  of  the  other;  or  (3)  a  mixture 
of  positive  and  negative  correlations,  due  to  the  complexity  of  the  con¬ 
ditions  governing  growth,  the  dissimilar  conditions  prevailing  in  different 
years,  and  the  differences  of  behavior  in  different  individuals  due  to  shading, 
crowding,  or  other  local  conditions.  Enough  data  were  secured  to  show  that 
the  third  of  these  hypothetical  cases  is  apparently  the  one  characterizing 
the  Monterey  pine.  In  tree  A  there  is  a  considerable  degree  of  correlation, 
at  least  qualitatively.  In  tree  B  there  is  a  strong  negative  correlation  with 
respect  to  the  growth  for  1918  and  1917,  and  a  positive  correlation  in  the 
following  years.  In  tree  C  there  is  an  alternation  of  positive  and  negative 
correlations  in  the  successive  years.  Trees  D  and  E  show  similar  irregular 
behavior.  In  tree  F  there  is  a  close  correlation  for  two  successive  intervals, 
followed  by  a  sharp  negative  correlation  in  the  two  succeeding  intervals. 
The  exceptionally  great  growth  in  height  in  1918  was  accompanied  by  a 
very  small  growth  in  diameter. 

In  comparing  the  graphs  for  the  diameter-growth  at  the  base  of  the  trunk 
and  those  for  growth  in  diameter  halfway  up  the  trunk,  it  will  be  seen  that 
there  is  a  close  correlation  in  all  cases  except  the  last  interval  in  tree  F,  in 
which  an  increase  of  basal  diameter-growth  was  accompanied  by  a  decrease 
of  mid-stem  diameter-growth. 

DIAMETER-GROWTH  AT  DIFFERENT  HEIGHTS  IN  THE  TRUNK. 

Our  knowledge  of  the  diameter-growth  of  individual  trees  and  our  infor¬ 
mation  regarding  the  total  increment  of  forest  stands  have  been  based 
chiefly  on  data  secured  below  a  level  of  5  feet  on  the  trunk  of  the  tree.  Such 
data  include  increment  borings,  caliper  measurements  made  at  breast- 
height,  and  the  great  majority  of  the  dendrograph  records  thus  far  secured. 
In  order  to  secure  material  for  comparing  the  relation  of  height  and  diam¬ 
eter  growth  in  a  large  tree,  and  for  comparing  the  diameter-growth  at 
different  heights,  a  special  investigation  was  undertaken. 

After  careful  selection,  a  tree  was  found  which  had  reached  the  mature 
height  of  20  meters,  but  had  not  yet  lost  the  excurrent  habit  of  branching 
which  is  typical  of  the  early  life  of  the  pine.  This  tree  was  situated  on  a 
slope  overlooking  the  sea  4  miles  south  of  Carmel,  California,  and  was 
growing  in  a  normal  stand  of  trees  of  approximately  the  same  diameter. 
The  tree  was  felled  in  the  early  part  of  July  1921,  and  the  trunk  was  care¬ 
fully  cut  away  on  one  side  by  a  skilled  woodsman  until  the  median  line  of 
pith  was  revealed.  The  trunk  was  then  cut  transversely  into  sections  1 
meter  long,  and  both  the  longitudinal  and  transverse  sections  were  smoothed 
so  as  to  make  easy  the  following  and  identification  of  all  rings  of  growth. 

The  age  of  this  tree  was  found  to  be  38  years.  The  diameter  at  the  stump 
was  43.5  cm.  outside  bark  and  39  cm.  inside  bark.  The  diameter  18  meters 
above  the  stump  was  7.5  cm.  outside  bark  and  7.2  cm.  inside  bark.  The 
height-growth  of  1921  had  been  14  cm.,  that  of  1920,  6  cm. 

The  thickness  of  the  individual  rings  was  measured  at  each  of  the  20 
transverse  sections.  In  all  cases  the  measurements  were  made  along  either 


98 


GROWTH  RECORD  IN  TREES. 


two  or  three  radii  and  in  the  case  of  the  stump  along  six  radii,  and  the  aver¬ 
ages  recorded.  The  entire  growth  history  of  the  tree  was  thus  secured,  by 
years  and  by  heights  from  the  stump,  and  in  every  section  the  longitudinal 
face  of  the  trunk  was  used  to  verify  the  identity  of  the  rings.  The  figures 
secured  are  shown  in  table  4,  being  increments  in  radius  only  and  requiring 
to  be  doubled  to  secure  diameter  increments. 

The  period  of  most  rapid  growth  in  height  was  the  first  10  years  in  the 
life  of  the  tree,  from  1884  to  1894,  in  which  it  attained  a  height  of  10  meters. 
In  the  16  years  from  1894  to  1910  there  was  an  additional  height-growth  of 
8.8  meters.  In  the  11  years  from  1910  to  the  felling  of  the  tree  the  growth 
in  height  was  only  1.2  meters.  The  greatest  increment  in  diameter  in  a 
single  year  was  33  mm.  recorded  in  1891  at  a  height  of  5  meters,  and  in 
1892  at  a  height  of  3  meters,  these  cases  being  respectively  at  and  near  the 
center  of  the  tree.  The  greatest  increases  in  diameter  occurred  during  the 
first  half  of  the  life  of  the  tree  and  during  the  period  which  was  also  marked 
by  the  greatest  height-growth.  During  the  last  10  years,  and  after  the 
growth  in  height  had  become  very  slow,  the  radial  increments  of  growth 
had  become  small,  exceptional  cases  indicating  a  diameter  increase  of  8  mm., 
the  majority  of  cases  an  increase  of  less  than  5  mm.,  and  very  many  cases 
diameter  increments  of  less  than  2  mm.  An  inspection  of  the  table  of  annual 
growth  increments  shows  that  the  greatest  radial  increase  in  a  given  year 
is  generally  found  in  the  upper  half  of  the  trunk  and  most  commonly  within 
5  or  6  meters  of  the  top.  There  are  a  few  exceptional  cases,  as  1901,  1904, 
and  1913,  in  which  the  greatest  growth  was  near  the  base  of  the  trunk,  but 
in  each  of  these  cases  there  is  a  region  of  active  growth  near  the  top  in 
which  a  submaximum  may  be  found.  An  inspection  of  the  table  with 
respect  to  the  year  of  greatest  growth  at  a  given  cross-section  of  the  trunk 
will  show  that  this  is  commonly  to  be  found  at  or  near  the  center  of  the 
trunk,  and  very  rarely  more  than  four  rings  from  the  center. 

A  marked  characteristic  of  the  Monterey  pine  is  the  frequent  alternation 
of  light  and  heavy  rings  of  autumnal  wood,  the  light  ring  invariably  lying 
nearer  to  the  heavy  ring  outside  it  than  it  does  to  the  ring  inside  it.  The 
existence  of  double  rings  necessitates  caution  in  determining  the  age  of 
examples  of  the  Monterey  pine,  but  there  are  few  cases  in  which  the  com¬ 
parative  heaviness  of  the  ring,  and  an  examination  of  the  entire  circum¬ 
ference  of  the  section,  will  not  definitely  establish  their  nature.  In  the  case 
of  the  bisected  trunk  the  longitudinal  faces  afforded  an  additional  means  of 
making  sure  as  to  the  dating  of  all  rings.  In  making  the  measurements,  a 
record  was  kept  of  all  years  in  which  there  was  an  intercalary  ring,  and 
these  are  indicated  in  the  table  by  heavy-faced  numerals.  It  will  be  seen 
that  the  double  nature  of  the  growth  for  a  given  year  is  not  always  apparent 
at  all  levels  in  the  tree.  In  1897,  for  example,  there  was  a  double  ring  from 
the  stump  up  to  a  height  of  7  meters,  and  the  sections  from  8  to  12  meters 
failed  to  show  any  indication  of  double  rings.  In  other  cases,  as  1903  and 
1905,  there  were  weakly  developed  intercalary  rings  at  the  base  of  the  trunk 
and  more  strongly  developed  ones  toward  the  top.  The  nature  of  the  double 
rings  will  be  discussed  further  in  a  later  section. 

The  data  presented  in  table  13  afford  an  opportunity  to  determine  the 
relative  thickness  of  the  cone  of  wood  laid  down  at  different  levels  on  the 


MONTEREY  PINE  (PINUS  RADIATA). 


99 


trunk  in  a  given  year,  and  also  to  compare  the  relative  thickness  of  any 
two  layers  at  different  levels.  As  already  noted,  the  maximum  thickness  is 
usually  in  the  upper  part  of  an  annual  cone  and  in  general  the  thickness  of 
the  upper  half  is  greater  than  that  of  the  lower  half.  The  difference  between 
the  thickness  of  the  upper  and  lower  portions  was  less  in  the  early  life  of 
the  tree  and  became  greater  during  its  last  ten  years.  A  comparison  of  the 


Table  13. — Average  thickness  of  annual  rings  of  growth  in  bisected  Monterey  Pine  measured 

on  sections  taken  at  10-meter  intervals. 


The  figures  in  the  headings  represent  the  height  (in  meters)  from  stump. 
The  figures  in  the  body  of  the  table  represent  the  growth  in  centimeters. 


1  1 

19.8  19.6  18.8 

1  1 

© 

00 

rH 

17.0 

16.0 

15.0 

14.0 

13.0 

12.0 

11.0 

10.0 

9.0 

8.0 

7.0 

6.0 

5.0 

4.0 

3.0 

2.0 

1.0 

o.ol 

1921 

2.0 

1.5 

2.2 

0.7 

1.0 

1.0 

1.0 

2.0 

1.0 

0.4 

0.5 

0.4 

0.3 

0.2 

0.1 

0.2 

0.2 

0.3 

0.5 

0.5 

0.5 

0.5 

1920 

.... 

3.0 

2.3 

2.4 

1.4 

1.2 

1.0 

1.8 

0.7 

0.4 

0.4 

0.2 

0.4 

0.2 

0.1 

0.2 

0.2 

0.3 

0.5 

0.5 

0.5 

0.7 

1919 

.... 

2.5 

3.0 

2.5 

2.1 

2.1 

1.5 

1.8 

0.1 

0.6 

0.5 

0.5 

0.9 

0.2 

0.2 

0.1 

0.2 

0.3 

0.5 

0.5 

0.4 

0.5 

1918 

2.4 

2.5 

2.0 

2.4 

0.9 

1.6 

1.5 

.9 

1.2 

1.1 

1.7 

0.4 

0.7 

1.0 

0.4 

0.5 

0.5 

0  4 

1  2 

1  2 

1917 

2.7 

J  2.7 

3.0 

2.5 

1.9 

2.2 

1.9 

1.6 

1.5 

0.9 

2.4 

0.7 

0.8 

1.9 

1.6 

1.2 

1.1 

0  8 

1  0 

1  3 

1916 

1.6 

1.4 

1.9 

1.5 

2.5 

2.8 

3.6 

3.5 

4.0 

2.8 

3.2 

1.0 

1.2 

1.7 

.8 

1.6 

1.5 

1.0 

1  9 

2  1 

1915 

1.5 

!  1.8 

1.9 

1.9 

3.5 

3.6 

3.8 

3.7 

4.0 

2.6 

2.8 

2.5 

1.8 

2.1 

1.8 

2.0 

2.5 

2  0 

3  0 

2  9 

1914 

1.0 

1.2 

2.0 

3.0 

4.8 

4.6 

3.9 

3.5 

3.1 

0.9 

1.6 

2.0 

2.7 

3.0 

2.5 

2.3 

3.0 

3.0 

2  1 

2  0 

1913 

1.0 

2.0 

0.8 

1.5 

2.0 

2.1 

4.1 

2.2 

2.5 

1.5 

3.0 

1.5 

2.0 

1.6 

2.0 

1.7 

1.5 

4.5 

2  0 

1  5 

1912 

0.5 

2.0 

1.8 

2.2 

3.7 

3.0 

3.0 

2.5 

2.4 

1.5 

2.5 

1.5 

2.1 

1.7 

2.2 

1.6 

2.1 

1.5 

1  5 

2  0 

1911 

1.5 

1.2 

3.0 

2.6 

3.0 

2.8 

3.2 

2.7 

2.0 

2.5 

2.7 

1.7 

1.7 

1.5 

1.5 

1.5 

1.7 

2.5 

2  0 

2  0 

1910 

1.5 

1.4 

2.2 

2.3 

3.8 

4.6 

3.8 

2.6 

3.0 

2.0 

2.7 

2.4 

2.2 

2.3 

2.4 

1.9 

2.0 

3  0 

2  1 

1  6 

1909 

3.0 

3.0 

3.2 

4.2 

3.2 

3.9 

3.2 

3.0 

O.S 

1.0 

2.0 

2.8 

2.7 

2.4 

1.8 

2.0 

2  9 

2  5 

2  4 

1908 

3.6 

3.0 

4.3 

4.0 

3.5 

6.5 

6.2 

7.0 

5.0 

6.0 

1.0 

1.2 

1.0 

1.1 

1.2 

1.0 

3  0 

2  5 

2  6 

1907 

3.0 

3.5 

4.1 

6.0 

6.1 

7.0 

7.5 

8.0 

7.7 

6.8 

4.5 

6.4 

5.2 

4.6 

3.8 

3.6 

1  2 

1  6 

3  8 

1906 

2.1 

4.0 

7.0 

7.0 

6.2 

7.0 

7.5 

6.5 

6.0 

5.0 

6.5 

5.6 

5.8 

5.0 

5.5 

3  5 

4  5 

6  0 

1905 

3.0 

4.5 

4.6 

6.5 

5.0 

5.5 

5.6 

1.4 

1.5 

6.2 

6.8 

4 . 5 

6.0 

5.0 

6.0 

5.5 

5  0 

6  4 

1904 

7.0 

3.6 

4.4 

5.5 

4.9 

4.5 

4.5 

4.3 

3.5 

1.4 

1.5 

1.0 

1.0 

1.0 

1.0 

7.0 

7  1 

4  0 

1903 

5.0 

3.1 

3.4 

5.0 

4.8 

5.0 

5.0 

4.5 

3.5 

5.0 

2.6 

2.5 

2.0 

2.5 

3.5 

4  6 

3  9 

1902 

3.5 

4.4 

4.5 

6.0 

7.0 

4.8 

4.0 

3.5 

3.0 

3.5 

3.5 

3.0 

3.5 

3  2 

3  0 

5  1 

1901 

6.0 

5.5 

3.0 

2.5 

5.6 

6.0 

5.5 

4.5 

4.5 

4.8 

5.0 

3.2 

3.5 

4  0 

4  3 

6  2 

1900 

7.5 

5.0 

4.5 

5.0 

6.0 

4.0 

5.5 

5.4 

5.0 

5.0 

4.2 

4.8 

5  5 

5  0 

2  0 

1899 

4.5 

4.0 

4.1 

4.5 

5.2 

6.0 

4.5 

4.0 

5.2 

4.2 

4.5 

3  4 

5  0 

3  0 

4  2 

1898 

5.8 

8.0 

9.8 

3.5 

4.5 

5.6 

4.8 

5.6 

4.8 

4.5 

4.0 

5.0 

4  1 

3  5 

1897 

4.0 

5.0 

9.0 

8.0 

4.5 

4.5 

3.5 

3.0 

3.0 

5.0 

3.5 

3  0 

3  2 

1896 

6.0 

6.5 

8.5 

8.8 

8  0 

6.5 

10.3 

8.7 

9.5 

8  0 

9  0 

8  5 

1895 

8.0 

10.5 

9.5 

10.5 

11.2 

9.0 

7.5 

7.5 

8  0 

6  0 

7  0 

1894 

5.5 

13.5 

12.0 

11.5 

12.3 

9.5 

10.0 

9.5 

9.5 

7  8 

9  0 

1893 

9.0 

11.5 

10.0 

9.8 

8.5 

8.0 

9  6 

6  5 

7  6 

1892 

9.0 

9.7 

11.0 

15.0 

14.0 

16.5 

13  0 

9  5 

12  5 

1891 

7.0 

12.0 

16.5 

13.5 

12.8 

11  0 

8  0 

7  7 

1890 

8.8 

12.0 

11.5 

10  5 

11  0 

1889 

9.0 

11.0 

10.5 

13  6 

14  5 

1888 

10  0 

6  5 

10  0 

1887 

7.0 

2.0 

6  7 

1886 

6  5 

1885 

4  7 

1884 

9  0 

1 

1 

relative  thickness  of  the  wood  of  any  two  years  discovers  many  cases  of 
great  variability.  In  fact,  it  is  seldom  that  a  ring  is  continuously  greater  or 
less  than  an  adjacent  ring  when  they  are  followed  for  several  meters  up  the 
trunk.  The  growth  for  1894  and  1895  shows  a  very  constant  relation,  in 
which  the  former  year  left  a  thicker  ring  than  the  latter  from  the  base  of 
the  tree  up  to  the  highest  level  at  10  meters,  where  there  was  a  reversal  of 
this  relation.  In  comparing  1903  and  1904,  the  latter  year  is  found  to 
exhibit  greater  growth  at  the  three  lowest  levels,  while  for  the  next  six  levels 
above  these  the  former  year  shows  a  much  greater  growth  than  the  latter. 
Numerous  cases  can  be  found  throughout  the  table  in  which  there  is  great 


100 


GROWTH  RECORD  IN  TREES. 


irregularity  in  the  relation  between  the  growth  of  two  adjacent  or  separate 
years. 

In  order  to  make  more  graphic  the  relations  between  the  annual  progress 
of  growth  at  different  heights  in  the  trunk,  figure  22  has  been  drawn  to  show 
the  average  increments  at  the  stump  and  at  heights  of  5,  10,  and  15  meters. 
The  four  graphs  in  this  figure  show  how  rarely  there  is  a  coincidence 
between  the  maxima  and  minima  of  growth,  and  how  frequently  there  is 
a  dissimilarity  of  pitch  between  the  lines  in  each  vertical  series,  indicating 
a  lack  of  uniformity  in  the  thickening  of  the  same  cone  of  wood  at  these 
levels.  There  is  a  somewhat  better  correspondence  between  the  graphs  for 
the  stump  and  the  5-meter  level  than  there  is  between  those  for  5,  10,  and 
15  meters.  This  indicates  that  the  portions  of  the  trunk  above  the  lowest 
existing  branches,  and  above  the  branches  which  existed  5  to  10  years  ago, 
may  have  had  their  growth  influenced  by  the  position  of  the  foliage  from 
which  their  supplies  of  metabolic  material  were  drawn. 


Fig.  22. — Graphs  showing  annual  increase  in  diameter  in  trunk  of  bisected  Monterey  pine  at 

stump  and  at  heights  of  5,  10,  and  15  meters. 


A  more  graphic  delineation  of  the  irregularity  in  thickness  of  certain 
annual  layers  of  growth  has  been  attempted  in  figure  23,  which  illustrates 
a  stump  6  meters  in  height,  from  which  a  sector  has  been  removed  so  as  to 
reveal  the  median  surface,  on  which  have  been  drawn  to  scale  the  thickness 
of  the  annual  layers  for  the  years  1903  to  1908.  It  is  obvious  from  this 
diagram  that  sections  of  the  trunk  made  at  any  two  levels  would  indicate 
very  dissimilar  marches  of  growth  from  year  to  year. 

In  the  summer  of  1923  a  second  pine  was  felled  and  examined  in  a  manner 
similar  to  that  employed  in  the  bisected  tree  that  has  just  been  described. 
This  tree  was  growing  in  close  proximity  to  the  Coastal  Laboratory,  on  the 
steep  inward  face  of  the  old  stabilized  dune  on  which  Carmel  is  situated. 


MONTEREY  PINE  (PINUS  RADIATA). 


101 


Its  height  was  55  feet  and  its  age  28  years.  The  tree  was  felled  by  a  cut 
6  inches  from  the  ground,  and  transverse  cuts  were  made  at  intervals  of  3 


Fig.  23. — Schematic  illustration  of  vertical  variation  in  thickness  of  annual  rings  of 

bisected  Monterey  pine  for  years  1903  to  1908. 


feet  throughout  the  trunk.  The  rings  were  so  legible  at  all  of  the  cuts  that 
bisection  was  necessary  only  in  the  case  of  the  lowest  piece.  In  table  5  are 
shown  the  average  measurements  of  the  thickness  of  the  rings  on  the  19 


102 


GROWTH  RECORD  IN  TREES. 


surfaces.  In  figure  24  are  shown  the  graphs  of  growth  at  the  stump  and  at 
heights  of  9,  18,  and  27  feet  from  the  stump. 

The  vigorous  condition  of  the  tree  is  attested  by  the  fact  that  it  had 
grown  in  height  at  an  average  of  3  feet  per  annum  for  the  last  21  years,  not 
yet  having  reached  the  stage  of  matured  crown.  The  statements  made  with 
regard  to  the  first  tree  hold  true  of  this  one  with  respect  to  the  times  and 
regions  of  most  active  wood  formation.  There  is  in  this  tree,  however,  a 
greater  uniformity  in  the  relative  thickness  of  the  various  rings  at  each 
level  in  the  trunk,  as  will  be  seen  by  a  comparison  of  figure  22  and  figure  24. 


Fig.  24. — Graphs  showing  increase  in  diameter  in  trunk  of  Monterey  pine  at  stump  and  at 

heights  of  9,  18,  and  27  feet. 


There  is  also  a  closer  correspondence  throughout  the  trunk  between  the 
annual  fluctuations  of  growth.  During  the  last  20  years  of  the  life  of  the 
former  tree  there  were  only  3  years  in  which  the  growth  graphs  corre¬ 
sponded  in  direction  at  the  four  levels.  In  the  last  10  years  of  the  latter 
tree  there  were  7  years  in  which  the  growth  graphs  corresponded  in  direction. 
There  are  nevertheless  some  conspicuous  cases  in  the  second  tree  in  which 
a  less  growth  or  a  very  slight  increase  of  growth  in  the  lower  half  of  the 
trunk  was  accompanied  by  a  marked  increase  over  the  preceding  year  in 
the  upper  half  of  the  trunk. 

The  factors  concerned  in  causing  the  observed  differences  in  wood  incre¬ 
ment  at  different  levels  in  the  same  year  are  probably  deep-seated  ones 


MONTEREY  PINE  (PINUS  RADIATA). 


103 


that  could  be  discovered  and  investigated  only  through  the  aid  of  a  much 
fuller  knowledge  of  the  physiology  of  the  tree  and  the  mechanism  of  the 
transport  of  foodstuffs  than  we  now  possess.  The  history  of  the  survival 
and  death  of  the  lowest  branches  is  also  concerned  in  these  differences.  It 
remains  to  be  learned,  also,  whether  such  irregularity  is  of  constant  occur¬ 
rence  in  the  Monterey  pine  and  whether  it  is  characteristic  of  other  pines 
and  of  other  tree  species  as  well.  No  literature  has  been  found  which  makes 
it  possible  to  institute  such  a  comparison. 

DOUBLE  RINGS  OF  GROWTH. 

The  only  piece  of  direct  evidence  as  to  the  nature  and  cause  of  the  double 
annual  rings  of  growth  has  been  secured  by  MacDougal  in  his  dendrographic 
records  for  the  Monterey  pine  for  1918.  In  that  year  in  mid-September 
there  occurred  an  exceptionally  early  and  heavy  rain  of  5.59  inches,  lasting 
for  3  days.  Although  the  growth  of  the  pine  had  slowed  down  almost  to  a 
standstill,  this  heavy  rain  caused  renewed  activity,  as  exhibited  by  the 


Fig.  25. — Graph  showing  September  rainfall  (solid  line)  and  percentages  of  cross-sections 
of  trunk  showing  double  rings  of  growth  for  corresponding  years  (dots) . 

dendrograph.  Increment  borings  taken  the  following  year  from  the  tree 
on  which  the  dendrograph  had  been  mounted  showed  that  a  second  annual 
ring  of  growth  had  been  formed,  with  its  thickness  corresponding  to  the 
dendrographic  measure  of  the  September  activity.  Boring  and  sections  of 
many  other  trees  have  shown  the  occurrence  of  a  secondary  ring  for  1918. 

The  probability  that  all  cases  of  double  rings  could  be  explained  by  the 
occurrence  of  late  summer  or  early  autumnal  rain  on  the  years  in  which 
the  secondary  rings  occur  led  to  an  effort  to  correlate  the  two  phenomena 
in  the  data  from  the  bisected  pine,  with  the  result  shown  in  figure  25.  It 
will  be  seen  that  the  higher  September  rainfall  of  1892  and  1904  did  not 
cause  an  increase  in  the  percentage  of  cross-sections  of  the  tree  showing 
double  rings  for  those  years.  The  absence  of  September  rain  in  1895  and 
in  1902  and  1903  was  concurrent  with  a  relatively  high  percentage  of  sec¬ 
tions  showing  double  rings  for  those  years.  Correlations  involving  the 
October  rainfall  alone  or  the  sum  of  the  September  and  October  rainfall 
are  no  stronger.  Further  investigation  will  be  required  to  determine  all  of 


104 


GROWTH  RECORD  IN  TREES. 


the  factors  involved  in  what  is  very  obviously  a  result  of  the  occurrence  of 
two  seasons  with  favorable  growing  conditions,  separated  by  several  weeks 
of  unfavorable  conditions. 

REDWOOD  (Sequoia  sempervirens). 

In  the  summer  of  1922  a  redwood  was  felled  and  the  trunk  bisected  longi¬ 
tudinally  and  then  cut  transversely  into  lengths  of  1  meter  each,  in  the  same 
manner  employed  in  the  pine.  The  redwood  was  growing  near  the  drainage¬ 
way  of  a  small  canon  tributary  to  Rocky  Creek,  at  a  distance  of  about  3 
miles  from  the  coast  and  about  17  miles  south  of  Carmel.  Like  so  many  of 
the  younger  redwoods,  the  origin  of  this  tree  was  as  a  sucker  from  a  large 
tree  no  longer  standing.  The  stump  of  the  tree  from  which  this  sucker  and 
three  accompanying  ones  originated  was  still  legible  and  indicated  that  it 
had  been  felled  at  the  age  of  75  years.  The  trunk  taken  for  bisecting  was 
17  meters  high  and  26  cm.  thick  at  the  stump,  which  was  cut  flush  with 
the  surface  of  the  ground.  The  age  was  15  years.  The  bole  was  straight 
and  indicated  a  vigorous  and  uninterrupted  growth. 

The  figures  for  annual  increments  of  radius  at  the  various  heights  are 
shown  in  table  14.  It  will  be  seen  that  a  fairly  uniform  growth  in  height 


Table  14. — Average  thickness  (in  millimeters)  of  annual  rings  of  growth  in  Monterey  pine  measured  on  sections 

taken  at  intervals  of  3  feet. 


of  a  little  more  than  1  meter  per  year  was  maintained  throughout  the  life 
of  the  tree.  In  four  of  the  1-meter  sections  of  the  trunk  the  age  was  the 
same  at  both  ends  of  the  section.  In  all  other  sections  the  lower  end  was 
one  year  older  than  the  upper.  The  maturing  of  the  crown,  and  the  accom¬ 
panying  decrease  in  rate  of  growth,  first  begin  in  the  redwood  at  a  greater 
height  and  age. 

During  the  first  five  years  the  greatest  growth  in  thickness  was  in  the 
basal  or  middle  portion  of  the  trunk,  but  after  the  sixth  year  it  is  to  be 
found  almost  invariably  in  the  uppermost  part  of  the  trunk.  In  the  exami- 


REDWOOD  (SEQUOIA  SEMPREYIRENS). 


105 


nation  of  each  transverse  section  the  maximum  growth  is  found,  in  all  cases 
but  one,  to  have  taken  place  near  the  center  of  the  trunk,  as  was  likewise 
the  case  in  the  pine. 

In  order  to  compare  the  redwood  and  the  pine  with  respect  to  the  com¬ 
parative  growth  behavior  at  different  elevations,  graphs  have  been  drawn 
for  the  redwood  which  are  shown  in  figure  26.  The  lowest  graph  shows  the 
annual  increments  of  radius  at  the  stump,  and  the  upper  graphs  show  the 
increments  at  3-meter  intervals  up  to  a  height  of  12  meters.  A  comparison 
of  these  graphs  with  those  for  the  pine,  in  figure  22,  shows  a  somewhat 
greater  uniformity  at  the  different  levels  in  the  redwood.  At  the  stump  and 
at  3  and  6  meters  there  was  a  progressive  slowing-down  of  growth  from 


Fig.  26. — Graphs  showing  annual  increase  in  diameter  in  trunk  of 
bisected  redwood  at  stump  and  at  heights  of  3,  6,  9,  and  12 
meters. 


1912  until  1917,  a  year  in  which  the  rate  was  low  throughout  the  trunk. 
From  1917  until  1920  there  was  an  increase  of  growth-rate  to  the  height 
of  9  meters.  There  are,  nevertheless,  some  conspicuous  irregularities  in  the 
several  graphs.  At  each  of  the  five  levels  it  will  be  seen  that  one  or  two 
years  are  required  to  bring  the  growth  rate  of  the  young  trunk  up  to  a  maxi¬ 
mum,  and  this  rate  is  scarcely  attained  again,  and  only  once  exceeded,  in 
the  later  growth  at  these  levels.  From  1916  until  1921  the  growth  was  very 
slight  at  3  meters,  although  a  normal  rate  was  maintained  at  the  stump 
and  at  6  meters.  In  1921  the  growth  at  the  stump  exceeded  that  of  1920, 
while  at  all  of  the  higher  levels  it  was  less  or  the  same. 

Double  rings,  similar  to  those  described  in  the  pine,  were  found  in  the 
redwood  in  the  outer  portion  of  the  trunk  at  levels  of  8  to  7  meters,  but 
were  not  discovered  in  wood  of  the  same  years  at  the  higher  levels. 


106 


GROWTH  RECORD  IN  TREES. 


In  view  of  the  difference  in  the  annual  march  of  growth  at  the  various 
levels  in  the  trunk,  it  would  seem  that  a  measure  of  a  given  tree  could  best 
be  secured  by  averaging  the  data  from  several  successive  elevations.  If 
such  an  average  were  taken  of  the  portion  of  the  trunk  that  lies  below  the 
largest  branches  that  survive  until  maturity  is  reached,  the  resulting  figures 
should  give  a  very  accurate  indication  of  the  annual  wood  increment.  In 
view  of  the  discrepancy  between  the  rate  of  growth  at  the  stump  and  at  the 
higher  levels,  such  an  average  should  have  greater  value  than  data  secured 
from  the  stump  section  only  in  determining  the  total  annual  growth  per¬ 
formance  of  the  tree. 

CORRELATION  OF  GROWTH  AND  RAINFALL. 

It  has  long  been  well  known  that  the  growth  of  plants  depends  upon  con¬ 
ditions  of  temperature,  light,  and  moisture,  and  upon  the  supply  of  mate¬ 
rials  for  the  manufacture  of  food.  For  a  plant  growing  in  its  natural 
environment  the  normal  fluctuations  of  these  conditions  will  result  in 
unequal  amounts  of  growth  in  a  given  unit  of  time.  There  is  rarely  justi¬ 
fication  for  attributing  inequalities  of  growth  under  natural  conditions  to 
the  fluctuations  of  a  single  environmental  condition.  So  complex  is  the 
interaction  of  the  several  conditions  that  the  fluctuations  of  one  must  always 
be  interpreted  or  investigated  in  terms  of  the  others. 

With  respect  to  the  influence  of  rainfall  and  temperature  on  the  growth 
of  trees,  there  is  some  evidence  that  very  similar  rates  of  growth  may  be 
maintained  by  the  same  tree  under  different  rainfall  conditions,  providing 
there  is  a  compensating  difference  in  temperature.  The  writer  has  shown1 
that  the  Arizona  yellow  pine  in  the  Santa  Catalina  Mountains,  in  southern 
Arizona,  maintains  nearly  the  same  average  rate  of  growth  at  6,000,  7,000, 
and  8,000  feet  elevation  up  to  the  age  of  175  years.  The  rainfall  of  the 
growing-season  is  nearly  twice  as  great  at  8,000  feet  as  it  is  at  6,000  feet, 
while  the  average  extremes  of  temperatures  are  10°  higher  at  6,000  feet  than 
at  8,000  feet.  The  failure  of  this  tree  to  accomplish  greater  growth  with  the 
greater  rainfall  at  8,000  feet  is  apparently  to  be  attributed  in  part  to  the 
lower  temperature,  although  the  shorter  growing-season  at  the  higher  alti¬ 
tude  is  also  a  factor  of  importance.  Individual  trees  growing  at  6,000  feet 
in  close  proximity  to  streams  exhibit  a  rate  of  growth  much  greater  than 
that  of  any  tree  at  8,000  feet. 

The  Monterey  pine  is  indigenous  to  a  region  in  which  there  is  a  very  low 
rainfall,  or  an  absence  of  rain,  for  four  months  in  the  middle  of  the  growing 
season.  For  this  tree,  and  for  almost  all  of  the  conifers  of  California,  Ari¬ 
zona,  New  Mexico,  Nevada,  Utah,  and  Colorado,  the  growing-season  pre¬ 
sents  longer  or  shorter  periods  in  which  the  water-supply  is  inadequate  for 
the  most  rapid  growth.  Since  these  periods  of  drought  or  semidrought  are 
coincident  with  temperatures  that  are  favorable  for  growth,  it  follows  that 
the  inequalities  of  rainfall  and  soil  moisture  from  year  to  year  subject  these 
trees  to  conditions  in  which  the  single  environmental  condition  of  water- 
supply  may  become  the  dominant  one  in  determining  the  total  growth  per- 

1  Forrest  Shreve.  The  density  of  stand  and  rate  of  growth  of  Arizona  yellow  pine  as  influenced 
by  climatic  conditions.  Jour,  of  Forestry,  15,  695-707.  1917 


CORRELATION  OF  GROWTH  AND  RAINFALL. 


107 


formance.  Douglass1  has  investigated  the  relation  of  rainfall  to  the  growth 
of  the  yellow  pine  near  the  lower  altitudinal  edge  of  its  range  in  the  vicinity 
of  Prescott,  Arizona.  In  data  covering  the  years  1870  to  1910  he  has  shown 
a  close  correlation  between  precipitation  and  the  thickness  of  the  annual 
rings.  The  material  investigated  by  Douglass  was  not  only  growing  near 
the  distributional  limit  that  is  placed  upon  the  yellow  pine  by  moisture 
conditions,  but  was  in  a  region  in  which  the  growing-season  is  characterized 
by  a  high  percentage  of  clear  days  and  by  a  relatively  regular  march  of 
humidity  conditions.  It  remains  to  be  determined  whether  such  a  close 
correlation  between  growth  and  precipitation  is  also  found  in  this  tree  in 
other  localities  which  are  not  so  near  its  moisture-controlled  distributional 
limit,  and  whether  in  other  trees  and  in  other  localities  the  conditions  of 
cloudiness,  temperature,  and  humidity  serve  to  modify  the  important  influ¬ 
ence  of  the  moisture  supply. 

An  adequate  investigation  of  the  influence  of  fluctuations  of  rainfall  in 
causing  inequalities  of  growth  in  the  Monterey  pine  should  be  based  upon 
a  large  body  of  data  with  respect  to  both  rainfall  and  growth.  Even  with 
the  small  amount  of  such  material  secured  in  the  present  investigation  it 
has  seemed  desirable  nevertheless  to  make  a  correlation  of  rainfall  and 
growth,  especially  as  it  is  planned  to  carry  on  a  further  investigation  of  the 
matter.  It  is  of  paramount  importance  to  determine  whether  rainfall, 
through  its  agency  in  replenishing  the  soil  moisture,  is  indeed  the  principal 
condition  responsible  for  fluctuations  of  growth  from  year  to  year,  even  in 
the  regions  where  it  appears  to  be  the  most  critical  condition  for  trees  and 
other  plants.  It  remains  as  a  possibility  that  we  shall  be  able  to  discover 
an  expression  of  moisture  conditions,  or  of  moisture  conditions  combined 
with  some  aspect  of  temperature,  by  which  we  will  be  able  to  demonstrate, 
much  more  exactly  than  at  present,  the  determining  influences  that  underlie 
the  annual  fluctuations  of  growth. 

CORRELATION  IN  INDIVIDUAL  TREES. 

In  view  of  the  difference  discovered  in  the  present  work  between  the 
annual  march  of  growth  at  different  levels  in  the  tree,  it  appeared  desirable 
to  learn  whether  a  closer  correlation  between  rainfall  and  growth  is  secured 
by  using  stump  data  or  by  using  the  average  data  for  the  growth  of  the 
entire  trunk.  It  is  also  important  to  determine  what  portion  of  the  growing- 
season  is  of  greatest  importance  in  wood  formation,  through  the  method 
of  determining  which  months  yield  a  rainfall  total  that  is  mostly  closely 
correlated  with  the  growth. 

A  rainfall  record  is  available  for  Monterey,  California,  covering  the  life 
of  the  investigated  trees  up  to  the  year  1911.  The  record  for  Carmel  covers 
the  years  1899  to  1922,  with  a  break  from  1907  to  1909.  In  the  year  for 
which  the  records  overlap  it  appears  that  the  precipitation  at  Carmel  is 
slightly  greater  than  that  for  Monterey.  It  is  unfortunate  that  there  are 
no  records  for  localities  in  closer  proximity  to  the  trees  with  which  the 
correlations  are  to  be  made.  The  bisected  pine  grew  7  miles  from  Carmel 

1  A.  E.  Douglass.  Evidence  of  climatic  effects  in  the  annual  rings  of  trees.  Ecology,  vol.  I, 
24-32.  1920. 


108 


GROWTH  RECORD  IN  TREES. 


and  10  miles  from  Monterey,  the  bisected  redwood  grew  17  miles  from 
Carmel  and  20  miles  from  Monterey. 

For  purposes  of  correlation  with  growth  the  rainfall,  graphs  have  been 
worked  out  which  are  shown  in  figure  27.  These  comprise  the  annual 
rainfall,  and  the  rainfall  for  the  following  portions  of  the  year,  in  each 
case  inclusive  of  the  months  mentioned — March  to  August,  January  to 
August,  February  to  September,  and  December  (of  the  preceding  year)  to 
September.  Each  of  these  graphs  is  drawn  to  cover  the  life  of  the  trees 
investigated,  and  is  formed  by  supplementing  the  Monterey  record  with 
that  for  Carmel. 


Fig.  27. — Graphs  showing  annual  rainfall  and  seasonal  rainfall,  for  periods  indicated, 
for  Monterey  (solid  line)  and  Carmel,  California  (broken  line). 

The  correlation  of  growth  with  rainfall  has  been  made  for  the  pine  and 
for  the  redwood,  and  in  each  case  the  growth  data  from  the  stump  section 
and  from  the  average  of  the  10  lowest  sections  have  been  used.  With 
respect  to  rainfall,  the  four  sets  of  growth  data  have  been  correlated  wTith 
the  total  rainfall  and  with  the  four  sets  of  seasonal  rainfall  mentioned 
above.  The  method  of  correlation  used  with  this  small  series  of  data  has 
been  the  simple  one  of  counting  the  number  of  cases  in  which  the  compared 
graph  of  growth  and  rainfall  agree  in  direction,  and  recording  this  in  terms 
of  the  percentage  of  years  showing  agreement.  For  example,  if  the  growth 
of  1891  was  greater  than  that  of  1890  in  a  particular  case,  and  the  rainfall 
of  1891  was  also  greater  than  that  of  1890,  the  agreement  was  recorded 
as  a  positive  correlation.  By  use  of  this  method  no  account  is  taken  of 
the  actual  numerical  relation  between  the  correlated  data.  If  a  doubling 


CORRELATION  OF  GROWTH  AND  RAINFALL. 


109 


of  the  rainfall  was  accompanied  by  a  doubling  of  growth  in  one  case  and 
by  a  very  slight  increase  in  another,  the  two  were  recorded  as  positive 
correlations.  More  intensive  work  on  this  problem  should  be  directed  to 
taking  account  of  the  quantitative  aspects  of  the  correlations. 


Fig.  28. — Graphs  showing  rainfall  (solid  line)  and  growth  in  diameter  of  Monterey  pine 
(broken  line)  and  redwood  (heavy  line)  for  corresponding  years.  Above,  rain¬ 
fall  for  December  and  September,  and  average  growth  of  trunks;  below,  annual 
rainfall,  and  growth  at  stump, 

The  growth  data  have  been  derived  from  the  figures  given  in  tables  13 
and  14,  and  the  rainfall  data  are  presented  in  tables  15  and  16.  In  figure 
28  is  a  graphic  comparison  of  the  growth  and  rainfall  data,  and  in  table  8 
are  given  the  percentage  of  correlation  in  all  cases. 

Table  15. — Average  thickness  (in  meters )  of  annual  rings  of  growth  in  bisected  redwood  measured  on  section t 

taken  at  1 -meter  intervals. 


Height  from 
stump 
(meters). 

1921 

1920 

1919 

1918 

1917 

1916 

1915 

1914 

1913 

1912 

1911 

1910 

1909 

1908 

1907 

17 

4.5 

16 

6.0 

4.0 

15 

7.0 

6.9 

3.5 

14 

7.1 

8.8 

8.7 

13 

6.0 

6.2 

7.3 

5.1 

3.7 

12 

5.7 

6.9 

6.7 

7.5 

3.8 

3.2 

11 

6.9 

7.2 

7.2 

7.5 

5.5 

5.0 

3.3 

10 

6.1 

6.2 

6.4 

5.8 

3.7 

6.5 

6.7 

9 

6.2 

7.0 

6.0 

5.2 

3.8 

4.6 

6.5 

5.0 

4.2 

8 

6.6 

6.8 

6.3 

4.2 

3.0 

4.7 

6.5 

7.2 

9.0 

7 

6.6 

6.4 

6.1 

3.2 

2.7 

4.0 

4.5 

6.5 

7.8 

7.2 

6 

6.7 

8.0 

5.8 

4.2 

2.9 

3.5 

3.8 

5.3 

7.3 

8.3 

5.3 

5 

6.3 

6.0 

5.3 

4.0 

2.8 

3.2 

3.9 

5.0 

6.4 

9.0 

6.9 

4.9 

4 

7.2 

6.5 

5.3 

4.0 

2.6 

3.5 

4.6 

4.6 

5.2 

8.4 

8.7 

7.0 

3.9 

3 

7.2 

6.5 

4.9 

3.8 

2.7 

3.1 

4.9 

4.7 

5.6 

7.2 

8.2 

8.7 

8.1 

2 

7.8 

5.7 

4.8 

3.2 

2.2 

3.8 

4.5 

5.3 

4.8 

6.5 

6.6 

10.0 

9.1 

7.2 

1 

8.0 

8.0 

6.7 

3.5 

2.7 

3.7 

3.7 

4.2 

4.5 

6.0 

6.5 

8.5 

9.5 

11.7 

3.5 

0 

9.4 

8.2 

7.6 

3.7 

3.0 

5.6 

7.6 

6.4 

6.2 

8.0 

9.5 

9.4 

8.1 

10.1 

7.9 

In  the  correlation  of  growth  data  from  the  stump  sections  of  the  pine 
with  the  different  seasonal  groups  of  rainfall,  it  will  be  seen  that  in  all 
cases  there  are  very  nearly  the  same  number  of  agreements  and  disagree¬ 
ments,  represented  by  correlations  of  49  per  cent  to  54  per  cent.  The  corre- 


110 


GROWTH  RECORD  IN  TREES. 


lation  with  the  annual  rainfall  is  stronger,  65  per  cent,  in  spite  of  the  fact 
that  this  includes  rain  which  fell  after  the  cessation  of  the  growth  of  the 
year.  The  correlation  of  growth  for  the  entire  life  of  the  tree  with  the 
rainfall  for  the  period  from  December  of  the  preceding  year  to  September 
is  51  per  cent,  indicating  no  positive  relation  between  the  two  phenomena. 
When  the  first  20  years  of  the  life  of  the  tree  and  the  last  16  years  are 
separately  considered,  however,  there  is  a  decided  negative  correlation  for 
the  early  years  and  strong  positive  correlation  for  the  later  years. 


Table  16. — Rainfall  ( in  inches )  for  Monterey,  California. 


Year. 

Annual. 

Mar.-Aug. 

Jan.-Aug. 

Feb.-Sept. 

Dec.-Sept. 

1884 

26.47 

11.99 

18.93 

16.36 

20.12 

1885 

11.92 

2.34 

3.65 

2.43 

8.98 

1886 

12.30 

5.99 

10.22 

7.13 

11.95 

1887 

10.47 

1.81 

7.08 

6.98 

7.63 

1888 

14.54 

4.33 

9.37 

6.07 

11.83 

1889 

25.14 

5.95 

7.70 

6.89 

10.46 

1890 

15.96 

1.54 

11.88 

4.31 

23.52 

1891 

13.26 

3.48 

8.22 

7.27 

11.35 

1892 

17.01 

4.70 

6.86 

7.45 

12.86 

1893 

14.76 

7.65 

12.72 

11.11 

15.88 

1894 

16.49 

3.28 

8.58 

5.41 

10.53 

1895 

15.32 

3.41 

12.26 

5.96 

18.13 

1896 

14.21 

5.29 

8.65 

5.68 

10.38 

1897 

11.70 

4.50 

9.23 

8.25 

11.86 

1898 

7.24 

2.51 

4.48 

4.38 

6.52 

1899 

15.05 

4.21 

7.66 

4.87 

8.63 

1900 

11.77 

2.99 

4.99 

3.65 

6.38 

1901 

12.93 

2.63 

9.22 

7.36 

10.94 

1902 

14.60 

5.59 

11.27 

9.45 

11.79 

1903 

14.67 

6.78 

12.09 

8.66 

13.26 

1904 

18.34 

6.23 

10.17 

11.75 

13.33 

1905 

21.63 

9.23 

17.08 

13.69 

20.14 

1906 

25.03 

7.56 

15.64 

10.68 

16.66 

1907 

28.98 

11.16 

20.41 

13.74 

28.55 

1908 

12.21 

1.87 

9.21 

4.65 

14.12 

1909 

28.39 

4.29 

20.43 

9.38 

22.04 

1910 

12.35 

3.60 

9.82 

4.82 

15.38 

1911 

25.39 

6.92 

21.86 

12.65 

22.41 

In  using  the  average  growth  data  from  the  10  lowest  trunk  sections  it 
is  found  that  the  correlation  with  the  annual  rainfall  is  63  per  cent,  or 
almost  identical  with  the  65  per  cent  found  for  the  stump  data.  In  the 
case  of  all  periods  of  seasonal  rainfall  there  is  a  negative  correlation  with 
the  average  growth  of  the  trunk.  Even  the  growth  of  the  last  16  years 
shows  in  this  case  a  correlation  of  50  per  cent,  indicating  that  the  rainfall 
conditions,  which  appear  to  have  been  significant  in  the  growth  of  the  tree 
so  far  as  concerns  the  stump  record,  were  without  importance  to  the  forma¬ 
tion  of  wood  in  the  tree  as  a  whole.  In  brief,  when  the  rainfall  of  the 
period  most  nearly  coinciding  with  the  growth-season  for  Monterey  pine, 
and  embracing  the  rain  of  the  month  preceding  the  commencement  of 
growth,  is  correlated  with  the  average  growth  of  the  entire  trunk  up  to 
30  feet,  the  result  indicates  that  the  precipitation  exerts  no  influence  upon 
growth. 


CORRELATION  OF  GROWTH  AND  RAINFALL. 


Ill 


For  the  redwood  the  correlation  of  stump-growth  with  the  annual  rainfall 
is  64  per  cent,  and  is  the  same  in  the  case  of  the  February  to  September 
rainfall.  As  in  the  pine,  the  negative  correlations  are  in  the  majority  for 
the  shorter  periods  of  seasonal  rainfall.  When  stump-growth  is  correlated 
with  the  rainfall  for  the  period  from  December  to  September,  there  is  a 
correlation  of  71  per  cent,  indicating  that  the  late  rain  of  the  winter  is  of 
considerable  significance  in  the  growth  of  this  tree  during  the  succeeding 
spring.  The  average  growth  data  for  the  10  lowest  sections  of  the  redwood 
show  a  weaker  correlation  with  all  but  one  of  the  seasonal  groups  of  rainfall 
than  do  the  data  from  the  stump  alone.  With  the  annual  rain  and  with 
the  December  to  September  rainfall  the  correlation  is  the  same,  62  per  cent. 
Contrasting  the  correlations  for  the  pine  and  the  redwood,  for  both  groups 
of  growth-data,  gives  51  per  cent  for  the  former  tree  and  71  per  cent  for 
the  latter  on  stump  data,  and  40  per  cent  for  the  former  and  62  per  cent 
for  the  latter  on  trunk  data.  This  indicates  that  rainfall  is  of  more  impor¬ 
tance  in  determining  the  rate  of  growth  of  the  redwood  than  it  is  in 
influencing  that  of  the  Monterey  pine. 

CORRELATION  IN  GROUPS  OF  TREES. 

It  was  desired  to  make  a  somewhat  more  extended  examination  into 
the  possibile  relation  of  precipitation  to  growth  by  using  data  on  the  growth 
of  a  larger  number  of  trees.  The  use  of  measurements  from  a  very  large 
number  of  stumps,  such  as  are  often  available  after  logging  operations, 
gives  no  opportunity  to  determine  the  character  of  the  trees  that  have  been 
felled.  Those  with  mature  and  immature  crowns  must  be  taken  together, 
those  growing  alone  and  those  more  or  less  suppressed  by  neighboring  trees, 
those  that  are  perfect  and  those  that  show  obvious  signs  of  damage  by 
storm  or  lightning.  It  is  only  by  the  use  of  a  very  large  body  of  such  data 
that  a  good  set  of  averages  can  be  secured,  in  which  the  results  from  the 
defective  trees  are  suppressed  by  a  supposedly  larger  number  of  data  from 
trees  in  vigorous  and  perfect  condition.  With  these  considerations  in  mind, 
it  was  decided  to  secure  data  by  means  of  an  increment  borer  from  a  small 
number  of  trees,  all  possessing  perfect  excurrent  crowns,  all  of  nearly  the 
same  size  (20  cm.  diameter),  all  growing  in  the  same  type  of  soil  and  the 
same  topographic  site,  in  close  proximity  to  each  other  and  to  the  rainfall 
station  for  Carmel.  It  is  believed  that  such  data  afford  the  optimum  basis 
for  comparison  of  growth  with  environmental  conditions.  In  addition, 
measurements  were  made  of  the  stumps  of  four  large  trees  of  approximately 
the  same  size  (60  to  68  cm.)  that  had  been  felled  adjacent  to  the  six 
small  trees. 

In  figure  29  are  shown  the  graphs  of  annual  march  of  growth  in  the  six 
small  trees,  together  with  the  rainfall  for  December  to  September.  Although 
these  trees  were  living  under  as  nearly  identical  conditions  as  is  possible 
under  a  state  of  nature,  it  will  be  noted  that  there  is  not  a  close  corre¬ 
spondence  between  their  growth  records.  In  the  19  years  covering  the  life 
of  the  youngest  of  the  group  there  were  only  6  years  in  which  all  six  of  the 
trees  rose  and  fell  together  in  their  change  of  total  growth  from  year  to  year. 
It  is  worth  noting  that  in  all  of  these  six  cases  the  graphs  of  growth  rose  or 


112 


GROWTH  RECORD  IN  TREES. 


fell  in  accord  with  the  graph  of  rainfall.  The  added  lengths  of  life  of  the 
six  trees  are  108  years.  Out  of  the  108  cases  in  which  the  growth  could  be 
compared  with  rainfall,  it  was  found  that  there  were  68  cases  in  which 
there  was  a  positive  correlation  between  them,  amounting  to  62.9  per  cent. 
In  the  case  of  the  four  large  trees,  the  total  length  of  life  was  112  years, 
and  of  these  there  were  57  in  which  there  was  a  positive  correlation  with 
rainfall,  amounting  to  50.9  per  cent.  These  figures  indicate  a  very  slight 


Fig.  29. — Graphs  showing  rainfall  for  December  to  September  and  course  of  growth 
in  6  small  trees  of  Monterey  pine.  Dots  at  top  indicate  years  of  accordant 
behavior. 


influence  by  rainfall  on  the  growth  of  the  younger  trees,  and  none  at  all 
on  the  older  trees.  This  is  directly  opposed  to  the  evidence  from  the  first 
bisected  pine,  in  which  there  was  a  much  stronger  correlation  in  the 
later  life  of  the  tree  than  in  its  earlier  life  (table  18). 

In  view  of  the  numerous  conditions  which  affect  the  growth  of  plants, 
it  appears  highly  probable  that  small  differences  in  rainfall  might  have 
their  influence  obscured  by  the  operation  of  some  of  the  other  conditions, 
and  that  the  influence  of  precipitation  would  be  exerted  most  clearly  in  the 


CORRELATION  OF  GROWTH  AND  RAINFALL 


113 


years  that  were  far  above  or  below  the  normal  rainfall.  On  this  basis  an 
examination  was  made  of  the  average  rates  of  growth  of  the  two  groups 
of  trees  in  the  four  wrettest  and  the  two  driest  years  between  1900  and  1922. 
The  results  are  shown  in  table  19.  For  the  small  trees,  the  growth  was  less 


Table  17. — Rainfall  {in  inches )  for  Carmel,  California. 


Year. 

Annual. 

Mar.-Aug. 

Jan.-Aug. 

Feb.-Sept. 

Dec.-Sept. 

1898 

10.37 

3.19 

6.43 

6.49 

14.42 

1899 

22.92 

8.22 

13.13 

8.78 

14.57 

1900 

18.75 

4.90 

9.58 

6.44 

12.49 

1901 

17.34 

3.91 

12.68 

9.42 

15.47 

1902 

18.13 

6.31 

13.34 

11.25 

14.01 

1903 

15.43 

4.16 

11.43 

6.82 

13.27 

1904 

24.54 

9.01 

14.90 

16.15 

18.55 

1905 

21.67 

9.44 

17.44 

17.07 

14.42 

1906 

29.44 

9.22 

18.01 

14.52 

20.01 

1907 

1908 

1909 

1910 

14.30 

4.18 

12.08 

5.21 

14.97 

1911 

27.07 

8.22 

22.97 

14.66 

23.64 

1912 

12.31 

7.31 

10.17 

7.94 

13.38 

1913 

15.47 

3.73 

7.87 

4.34 

8.79 

1914 

22.88 

3.63 

14.39 

8.39 

19.16 

1915 

24.09 

4.42 

17.97 

13.25 

25.12 

1916 

18.86 

1.20 

13.47 

5.79 

20.48 

1917 

9.91 

2.84 

8.41 

6.49 

11.33 

1918 

19.79 

4.04 

8.10 

13.00 

14.27 

1919 

14.04 

3.65 

8.89 

7.11 

10.74 

1920 

14.70 

5.21 

8.26 

7.61 

12.53 

1921 

21.20 

4.09 

10.87 

7.72 

13.97 

1922 

19.40 

4.27 

12.72 

9.93 

21.73 

Table  18. — Relation  of  rainfall  to  growth  of  Monterey  pine  and  redwood. 


[Qualitative  correlations  based  on  Monterey  rainfall  record  1884  to  1911  and  Carmel  record 

1912  to  1921.] 


Growth  data  from  stump 
section  only. 

Average  growth  data  from 
10  lowest  trunk  sections. 

Pine. 

Redwood. 

Pine. 

Redwood. 

Annual  rainfall . 

March  to  August . 

January  to  August . 

February  to  September . 

December  to  September . 

Same  for  years  1884  to  1904 . 

Same  for  years  1905  to  1921 . 

per  cent. 

65 

54 

49 

49 

51 

35 

70 

per  cent. 

64 

43 

50 

64 

71 

per  cent. 

63 

38 

34 

40 

40 

31 

50 

per  cent. 

62 

50 

25 

50 

62 

in  the  dry  year  1900  than  in  any  of  the  wet  years,  but  in  the  dry  year 
1913  it  was  greater  than  in  two  of  the  wet  years  and  nearly  as  great  as  in 
any  of  them.  For  the  large  trees,  the  growth  in  each  of  the  two  dry  years 
was  greater  than  in  any  of  the  wet  years.  In  order  to  secure  a  quantitative 


114 


GROWTH  RECORD  IN  TREES. 


measure  of  the  relation  between  growth  and  rainfall,  a  calculation  was 
made  of  the  growth  per  inch  of  rain  for  both  groups  of  trees  in  both  groups 
of  years.  These  figures  indicate  that  for  both  the  large  and  the  small 
trees  there  is  far  more  wood  formed  per  inch  of  rainfall  in  the  dry  years  than 
in  the  wet  ones. 


Table  19. — Growth  of  Pinus  radiata  (in  millimeters )  in  wet  and  dry  years. 
[Average  rainfall,  December  to  September,  14.17  inches.] 


Total  rain  December  to  September. 

Wet  years. 

Dry  years. 

1907 

1909 

1911 

1916 

1900 

1913 

28.55 

22.04 

22.41 

20.48 

6.38 

8.79 

Six  small  trees: 

Average  growth . 

4.6 

4.1 

3.9 

4.7 

2.7 

4.5 

Growth  per  inch  of  rain . 

.17 

.18 

.18 

.23 

.43 

.28 

Four  large  trees: 

Average  growth . 

6.2 

6.0 

5.3 

7.0 

7.8 

7.4 

Growth  per  inch  of  rain . 

.22 

.27 

.24 

.34 

1.22 

.84 

The  failure  to  find  a  strong  and  uniform  correlation  between  rainfall  and 
growth  in  the  wettest  and  driest  years  appears  to  be  one  of  the  most  impor¬ 
tant  pieces  of  evidence  secured  in  this  work  against  the  possibility  of  using 
the  growth  record  of  trees  as  a  universal  criterion  of  rainfall  conditions. 

CORRELATION  OF  GROWTH  AND  TEMPERATURE. 

The  absence  of  a  correlation  between  rainfall  and  growth  in  the  Monterey 
pine  suggested  the  possibility  of  a  closer  correlation  between  growth  and 
some  other  important  condition  affecting  it.  The  principal  of  these  is  tem¬ 
perature.  In  order  to  ascertain  whether  it  would  be  worth  while  to  under¬ 
take  a  serious  investigation  of  the  correlation  between  growth  and  tempera¬ 
ture,  a  single  determination  was  made  in  a  critical  case  that  fell  within  the 
range  of  the  climatic  records  for  the  Coastal  Laboratory.  It  happened  that 
the  rainfall  for  the  growing-season  of  the  years  1912  and  1921  was  nearly 
the  same  in  total  amount  (13.38  inches  and  13.97  inches  respectively)  and 
very  similar  in  its  seasonal  distribution.  In  these  years  the  growth  of 
the  four  large  trees  was  nearly  identical  (5.6  mm.  and  5.7  mm.  respectively), 
while  the  growth  in  the  six  small  trees  was  greater  in  1912  (3.2  mm.)  than 
in  1921  (2.6  mm.). 

The  temperature  datum  used  in  the  comparison  of  1912  and  1921  was  a 
summation  of  all  temperatures  above  40°  F.,  this  being  about  the  lowest 
minimum  temperature  at  the  time  of  the  year  when  growth  begins  in  the 
pine.  The  summation  was  made  by  tracing  the  thermograph  curves  on  stout 
paper  and  determining  the  total  area  by  weighing.  The  summations  were 
made  by  months,  so  as  to  make  it  possible  to  compare  the  totals  for  the 
months  of  most  active  growth  and  also  for  the  entire  growing-season.  The 


SUMMARY. 


115 


resulting  figures,  in  hour-degree  units,  are  shown  in  table  20,  together  with 
the  growth  and  rainfall  data  for  the  same  years.  In  both  groups  of  months 
the  temperature  summation  was  less  in  1912  than  in  1921,  but  the  difference 
is  not  very  great,  the  figures  for  1912  being  less  than  3  per  cent  below 
those  for  1921.  Such  a  slight  difference  is  to  be  expected  in  a  locality  with 
the  equable  maritime  climate  of  Carmel.  In  this  particular  instance  the 
group  of  small  trees  grew  more  in  the  year  with  the  smaller  temperature 
total.  The  almost  negligible  difference  between  the  growth  of  the  four  large 
trees  in  the  two  years  was  in  accord  with  the  small  temperature  difference, 
but  the  probable  error  in  both  determinations  is  great  enough  to  make  this 
correlation  mean  very  little. 


Table  20. — Growth  of  Pinus  radiata  in  relation  to  temperature. 
Summation  of  temperature  above  4-0°  F.  in  hour-degree  units. 


1912 

1921 

Average  growth,  six  small  trees . 

3.2 

2.6 

Average  growth,  four  large  trees. . . . 

5.6 

5.7 

Rainfall,  December  to  September. . . 

13.38 

13.97 

Temperature  summation: 

January  to  April . 

28,253 

30,261 

January  to  September . 

92,950 

94,969 

The  failure  to  secure  evidence  for  a  temperature  influence  in  the  two 
years  with  nearly  equal  rainfall,  and  the  discovery  of  such  a  close  corre¬ 
spondence  between  the  temperature  summations  for  the  two  years,  have 
discouraged  further  investigation  of  this  correlation. 

SUMMARY. 

The  Monterey  Pine  ( Pinus  radiata )  occupies  a  restricted  area  along  the 
coast  of  central  California,  and  has  been  investigated  in  the  region  of 
its  greatest  abundance  in  the  vicinity  of  Monterey,  California.  The  red¬ 
wood  ( Sequoia  semper virens)  has  been  investigated  south  of  Monterey, 
near  the  southern  limit  of  its  range. 

The  reputation  of  the  Monterey  pine  for  very  rapid  growth  is  based  on 
the  observation  of  exceptional  young  trees.  Out  of  125  stumps  examined, 
the  two  most  rapidly  growing  trees,  age  51  and  53  years,  had  made  an 
annual  average  diameter  growth  of  6  mm.  (0.25  inch).  The  greatest  growth 
observed  in  any  year  in  the  125  trees  was  a  diameter  increase  of  3.6  cm. 
(0.43  inch).  The  maximum  age  attained  rarely  exceeds  100  years. 

The  age-diameter  curve  for  the  Monterey  pine  is  nearly  a  straight  line, 
and  is  the  same  for  trees  growing  on  sand  and  trees  on  adobe  soil.  The 
fall  in  the  curve  that  is  commonly  found  in  other  trees  has  not  been  detected 
in  this  pine. 

In  young  trees,  5  to  15  years  old,  supernumerary  whorls  of  branches  are 
frequently  formed,  sometimes  formed  two  or  three  times,  on  the  shoot  of 
the  year.  Seedlings  from  10  to  19  cm.  in  height  add  an  average  of  86 
per  cent  to  their  height  in  a  single  year;  young  trees  130  to  139  cm.  in 
height  add  24  per  cent  to  their  height. 


116 


GROWTH  RECORD  IN  TREES. 


In  young  trees  100  to  200  cm.  in  height  from  40  per  cent  to  50  per  cent  of 
the  annual  growth  in  height  is  accomplished  before  the  end  of  March. 

In  young  trees  4.5  to  6  meters  in  height  there  is  no  correlation  between 
growth  in  height  and  growth  in  diameter. 

Trunks  of  pine  and  redwood  sectioned  at  intervals  of  1  meter  or  3  feet 
show  that  the  annual  march  of  growth  is  not  the  same  at  the  stump  and 
at  different  heights  in  the  trunk.  Growth  at  a  given  section  is  greater 
toward  the  center  than  towards  the  periphery,  and  in  a  given  year  is  greater 
within  5  or  6  meters  of  the  top  than  at  other  heights. 

Correlations  have  been  made  between  rate  of  growth  and  amounts  of 
annual  and  seasonal  rainfall.  The  growth  data  used  have  been  those 
from  the  stump  section  and  the  average  from  the  10  lowest  1-meter  sections. 
The  rainfall  data  used  have  been  the  totals  for  the  year  and  for  the  follow¬ 
ing  periods:  January  to  August,  February  to  September,  March  to  August, 
and  December  (of  the  preceding  year)  to  September.  The  results  indicate 
a  negative  correlation  between  growth  and  the  rainfall  of  the  shorter  periods 
in  the  growing-season,  and  a  small  positive  correlation  between  growth 
and  the  annual  rainfall.  Data  from  the  stump  show  no  correlation  with 
the  rainfall  of  the  period  from  December  to  September,  and  the  averaged 
data  for  the  trunk  show  a  negative  correlation  with  the  rainfall  of  the  same 
period.  The  correlation  with  annual  rainfall  is  the  same  for  Monterey 
pine  and  redwood,  but  the  correlation  with  the  rainfall  of  the  growing- 
season  is  greater  for  the  redwood. 

Correlations  of  growth  with  rainfall  were  made  in  six  small  and  four 
large  trees  of  Monterey  pine,  selected  for  equality  of  size  and  stage  of 
development  and  for  apparent  identity  of  environmental  conditions.  Using 
the  rainfall  of  December  to  September,  a  weak  correlation  was  found  in 
the  small  group  and  no  correlation  in  the  large  group. 

The  driest  years  at  Carmel  since  1900  have  had  about  one-third  as 
much  seasonal  rainfall  as  the  wettest  years.  In  the  six  small  trees  the 
average  growth  in  one  of  the  dry  years  was  less  than  in  any  of  the  wet  years. 

In  the  other  dry  year  it  was  greater  than  in  two  of  the  wet  years  and 
nearly  as  great  as  in  the  other  two  wet  years.  In  the  four  large  trees  the 
growth  was  greater  in  both  of  the  dry  years  than  in  any  of  the  four  wet 
ones.  The  growth  per  inch  of  rainfall  was  in  all  cases  much  greater  in 
the  dry  years  than  in  the  wet  ones. 

The  correlation  of  growth  with  temperature  in  two  years  with  nearly 
the  same  rainfall  shows  a  slight  negative  correlation  for  the  entire  growing- 
season  and  for  the  months  of  greatest  growth  in  the  case  of  the  small  trees, 
and  a  very  slight  positive  correlation  in  the  case  of  the  large  trees. 

The  collective  results  of  this  work  confirm  our  knowledge  of  the  depend¬ 
ence  of  growth  on  the  entire  constellation  of  environmental  conditions,  and 
indicate  that  the  annual  march  of  growth  is  not  correlated  with  the  march 
of  individual  conditions.  Future  investigations  may  make  it  possible  to 
formulate  a  composite  expression  of  the  leading  conditions,  with  which  the 
march  of  growth  would  be  in  close  correlation. 


